Proceed on the idea that Marcone- or even all mortals- have a small amount of talent (hence why rituals like Raith's canned summoning works). Say further that they can't develop it in a useful way because they lack the Sight. Further, developing skills takes confidence in possibility and the ability to refine the skill- when you first break a board you are using a lot more unfocused force and energy than you will in 10 or 20 years, even if you are less objectively strong by that point.
By that analogy, Namshiel is providing certainty that things are possible, the sensor suite to observe what Marcone is doing when he manipulates eldritch energies, and possibly through "VR training" giving Marcone the refinement of a lot of practice in a short span of time. Consider Marcone's shields. Very weak- to me, that represented how weak his ability at magic is compared to Harry's. He then used it with maximum cleverness and efficiency. The teapot dome? Namshiel slows time from Marcone's perspective, he works on tiny bits at a time that represent the maximum he can move, but he objectively does it so fast it is like he has expanded massive power quickly. He hasn't- instead of lifting the entire crate of sand in one mighty heave, he made the equivalent of millions of tweezer trips in seconds.
To me, emphasizing the weakness of Marcone's shields- and that he compensated by just stacking them as rapidly as possible for a kind of disintegrating defense-in-depth- was exactly what I'd expect of a low-powered but highly knowledgeable theoretician. He did the big effect (powerful effective shielding) with barely any use of energy (because he's very weak).
Regarding the burning- technically Harry didn't do anything to Bianca. He poured his mystic might into the ghosts of her victims like a loan, allowing them to have enough mystic energy to affect the physical world. That's why it neither violated the Laws nor the Accords. Harry didn't do anything to Bianca or her guests- he gave her prior victims the ability to do so. So no Accorded curbstomping of the White Council. A brilliant White Court vampire-style solution.
Killing Fomor minions with magic is a fascinating question, though. Once modified, are they still human? Are there any without at least gills? When does backlash occur? If you throw a fireball at someone, and they get capped seconds before your fireball hits, do you backlash? Or is it when you gather your power to kill? If you blast in a door with air or force, and an elderly gentleman has a heart attack from the noise, does that count?
I don't think we know, or should assume, Marcone is "very weak". Weaker than Harry in magical might, sure. But we don't know how much weaker he is than most. This is without adding Hellfire into the equation, and we know that adds a lot of muscle. Raw strength versus effective strength has also been shown to be a consideration. You can have incredible strength but if you're not efficient/effective at using it, it hardly matters. A classic example is Uriel versus Nicodemus. Uriel can end galaxies, universes. Yet is powerless to act against Nicodemus directly. So in many situations, Nicodemus is effectively stronger. In wizard terms, Harry has always had a big tank but the more efficient wizards get far more bang for their buck - Carlos is a great comparison in this. Where Marcone falls on the gradient is unclear, but I wouldn't be so quick to assume he is low-powered. As you point out, he is has clearly had enough training to be
highly efficient and effective. His biggest lack is experience, and he is gaining ground quickly.
Sorry, I probably wasn't clear. I was referring to the scene where Harry burns down Bianca's mansion with his spell. Not when he uses the ghosts to kill her. When Harry screamed "Fuego! Pyrofuego!" he was intending to burn the vampires. Yet he accidentally burned some of their victims too - some of which quite probably were alive up until his fire ended them. Intentions matter, but Jim has gone on and on (both in Q&As and throughout the series) about how it's the results that really count. Whether you or I agree personally or not (and that's rhetorical because I don't think this is the right section of the board for very personal views on such touchy subjects), it's how Jim has written the series. Given that, we can assume that if Dresden killed mortals even accidentally it still contributes to dark magic taint.
As for the Fomor Servitors, Carlos seems to imply the reason that the White Council regard them as protected by the First Law is that the risk is high enough that a person who killed such humanoids/demi-humans has a high chance of going Warlock. Whether that's an absolute universal thing is much harder to know. But I would say that if those servitors have Free Will, it probably counts.
Depending on how you define magic the Denarian's use it constantly. The classic example is that they are immortal in either form. If you mean that they don't throw fireballs then you're right, but that is merely a nod to the fact that there are only so many ways to represent magic in prose.
I'm saying something at a lower level. Butcher made magic a use it or lose it affair. And he used it in a fairly prominent way. He justifies Molly's talent and Charity's lack of talent using this device. You can always say that Marcone had latent powers, but by canon you use them or lose them. Marcone isn't particularly old but he's closer to Charity's age then to Molly's. This at least suggests that Butcher is using deceit to further the story versus having a coherent vision. For theory crafters there are some other implications as well. Take Malcolm. The fact that Eb said that he was a mortal is now meaningless. Because if Harry could miss Marcone, Eb could have missed something similar about Malcolm.
Susan triggered the curse when Harry murdered her. This is one of those arbitrary points in the story where Butcher uses the distinction to keep Harry from using magic to murder directly. He can cut Susan's throat but he can't strike her down with lightening.
On Chichen Itza there is a two minute span where Harry blanks out. It's meaningful because it is otherwise unnecessary. I suppose this is what they call Chekov's Gun. I think ID Harry or alternate Harry may not be as squeamish as our Harry and gave the curse a hard push with whatever Butcher is concealing about what Harry is.
I think the transformation the Denarians use is essentially the same as Werewolves like the Alphas use i.e. a single spell. From memory, the type of lupine theriomorph the Alphas are is just considered a classic werewolf. This is like a wizard who knows just one spell (how to become a wolf and turn back into a human again). Beyond that, most of what we have seen from Denarians is just sorcery i.e. destructive magic.
So I think in the broad sense you are right that all Denarians are inherently magical and use it all the time, because Fallen are creatures of magic. Given Harry's experiences with Lash I think that's a fair enough way to look at it. There were plenty of magical things she did with him and for him (and against him) that had nothing to do with him being a wizard. And I do agree there are only some many ways to show magic in prose, particularly given constraints that are required for novels to actually work.
But I was really just talking about those who behaved like wizards, for all intents and purposes. Those who used a wide variety of magical behaviours, spells, and disciplines to at least simulate wizard-like actions.
You are I think quite right that magic is a "use it or lose it" situation. But we don't know that Marcone (or others) don't use magic. We only get to see things from Harry's perspective, by and large. We don't know the things outside of that extremely limited viewpoint.
I think you're absolutely right about Eb being able to miss that Malcolm may well have been something more than mortal. That said...Jim has changed how soulgazes works (and why they do and don't work) several times. This is clearly due to his ideas changing over time, and then coming back to the old ones and trying to make them connect. It mostly doesn't affect things badly but occasionally it can create issues. For example, originally any being that didn't have a soul (i.e. wasn't a mortal human) couldn't be soulgazed. Then that changed to them not being able to be soulgazed like mortals, but Harry still had to be careful of what they could do through eye contact (i.e. psychic assault). Then it became their souls were not inside, but represented by what they did to the world around them. Yet we have Harry also being terrified of soulgazing some beings (who were not mortal) due to what it might do to his sanity. If Malcolm say were not mortal, he shouldn't have been able to be soul gazed period. Yet, where do transubstantiated mortals like Mac or Uriel in Skin Game fit? What about seeing Ursiel in Rasmussen? What about the forest people? Or the Fae?
I don't know that Susan can be held responsible for the curse triggering. She didn't take an action. Her lifeblood (in a very literal sense) triggered the curse. But she didn't cut her own throat, even if she did allow Harry to. Harry made the choice to kill her. Unfortunately, the consequences are on him. If you shoot someone, you can't blame the bullet or the powder.
I get that Butcher is trying to ensure Harry hasn't murdered her with magic directly. But he also has said not all of the consequences of magic come from people in grey cloaks too. I believe he was talking about there are universal, cosmic consequences to doing things. This shouldn't be surprising especially considering magic is considered the fundamental force of Creation.
You could well be right, Harry's Id might have driven the bus during that 2 minute blackout. I doubt that absolves him though. He and Id Harry are the same being, the same soul. Just different bits talking to each other.
I can see what you meant about stigmata now. I didn't see that at all myself, it's a very interesting interpretation. Jim does like to use things like that and make them fit into his story. Look at how he takes the concept of transubstantiation from the Bible and uses it in his series.
He never struck me as having any magical talent at all. Nor did he need it, he is a very clever cold
predatory crime boss. He began to lust for the power of the supernatural world the minute he witnessed Harry blowing the doors of his night club. A guy with real magical talent wouldn't have been shocked, Marcone was.. So he began his quest to acquire as much as he could, even though he was a mere vanilla human, he had amassed a great deal of influence and power[not the magical kind] that he used to great effect in bargaining with the supernatural world. He couldn't do magic so bought and surrounded himself with magical talent, he tried to buy Harry if you will remember and Harry refused. Now Marcone claimed to respect him for it, but who knows. Harry also made use of Marcone when he could as payment for pulling his goodies out of the fire in the case of the Loop and on Demonreach. Then the relationship started to fall apart when Marcone wouldn't help him in Changes. Then when Namshiel's coin fell into his lap in Small Favor, it presented a temptation that ultimately Marcone couldn't turn away from. Though he may live to regret it, as the old Chinese curse says,"be careful for what you wish for, you may get it."
He might have been shocked because it was a 6'9" angry wizard who was a lot stronger than him, and not many had the balls (or insanity) to attack him openly in his territory. He also just could have been scared. After all, Harry has scared plenty of magical humans and monsters too. And I think it's clear that Marcone DOES need magic, otherwise why would Jim write it in? Marcone could hardly be expected to survive all the supernatural encounters he has just vanilla. He's always had more on the ball than most expected. Not to mention, his heavyweight showdown with Harry has been on the cards since Storm Front.
Jim said smart wizards like Cowl are very careful about giving ANY information out, as wizards can use just about anything to get to another wizard. Information is a weapon after all, especially with wizards. Elaine has managed to keep of the Council's radar quite well, and fooled them about her real strength. Or most of them at any rate. It's an advantage against them.
Perhaps Marcone was just that careful. Perhaps not.
The idea behind why Mab was so bound and determined to have Harry as her Knight has probably changed over the course of the series. The current answer might be that she knew why Harry was created.
My crack theory that she became Mab to make sure that he can do what he will need to do. Whatever that might be.
Take the marriage to Lara. Mab says decisions she made while mortal keep her from marrying Lara. In my crack scenario she couldn't do it because she knows Harry has to. And she knows this because someone told her.
There are other things going on in the background as well.
Vadderung suggesting that this has all happened before, when he says that perhaps Harry had already kept the incursion on Demonreach from releasing the prisoners. This suggests a possible once through time loop.
Vadderung telling Harry Margaret's location so Harry can go and rescue her and then accepting no payment.
Members of the Senior Council so badly frightened that they will not explain what's going on.
Butcher introducing the idea that Alfred is concealing something.
Bonea as a new talking head.
This is my crack theory. Yours might be better and if so I may embrace it and take it to heart.
All interesting points. I like it. So to be clear, the theory is that Harry's whole life is a time loop around the end of the world? Perhaps all of human history? Essentially an ontological paradox?