Good point on mook rules. The Raven Mockers have already gotten a nickname of Raven Mookers, when they aren't called Raven Knockers due to the fact they're naked and sometimes female (you'd be surprised at the boob jokes a half female group will still make). They're pretty weak willed and even the original myths point out how easily they can be killed or controlled by more powerful witches (all supernatural baddies were called witches by the Cherokee), so it'd make sense to get a "discount" when dominating them. Of course, what's good for the goose is good for the gander. I hope my PCs will be clever enough to realize how easy it is to control them and try to turn that against my villain.
The book actually does say that the first two steps can be done separate, and even recommends it on page 272.
I'll keep the alternate rules in mind for when/if my players start to abuse thaumaturgy, but they're really new right now and having more trouble than I am grasping the rules. Throwing in house rules is all well and good for experienced groups, but it's best for beginners if we're all (literally) on the same page.
Edit: I'm working on a few other spells for my villain. I have to spoiler this part:
I need to know if it's possible to establish an alternate means of sympathetic connection. Harry knows about true names and things like hair clippings, but my guy's paradigm uses traditional hoodoo which also includes laying down tricks. There's different ways to do this in hoodoo, such as taking a pinch of dirt they left their footprint in. If this is possible, it's potentially really dangerous and broken. Then again, in modern times how often do we step in dirt that could leave a good enough footprint?
Alternately, you can do standard sympathetic magic backwards by making a ritual focus with a bit of you in it-such as fingernail clippings or pubic hair (ew)-then either secreting it about their person or tricking them into taking it (good trap for thieves). Obviously, this one is more risky since a wizard who survives your trick is likely to find the fingernail clippings and turn it around on you, but it's a method that most may not ever see coming.
Do you think either of these could provide the required sympathetic connection for a spell?
All good points and I see why you might not want to do this from a games-perspective. From a story perspective, it's some nice new toolkits to use and be really unexpected.
The more I think about it, the less "broken" it seems, because of the inherent limitations to these methods. For instance, for the footpath magic you need to have dirt that would maintain a footprint. You also have to be close enough behind the target to take a sample before someone else treads on it, and you have to be absolutely sure it's them. Take a footpath link after Harry's battle at wrigley field, and you could accidentally kill Matt Garza. I see this method as simply too impractical to be of any use in your average city, but out in the country or if you really go through a lot of trouble to set it up, maybe.
As for the "hiding a spell target on someone" method, I actually don't see how that is much worse than the classic "haircut mugging" method. Plus, you're handing your enemies a loaded gun with your name on it. This method I see as not being popular simply because it is so risky. You'd better make the first shot count, or it's coming right back at you.
As for issues with paradigm...the books aren't 100% accurate because they are rife with Harry's own biases and assumptions. He knows how to do it, and doesn't consider there could be another way because those ways were never taught to him or were simply impractical. Using an indirect link may be possible, just like using a mother's blood to find her daughter.
By the same token, sending the spell from the whole to the part seems to me like just an inversion of the standard method of sending it from the part to the whole. You're not targeting yourself, you're targeting part of you at another location. Actually, it may make sense to restrict this to only certain types of spells. Obviously, transforming or mind-controlling someone because they have your fingernail clippings might not work. On the other hand, a targeted summoning at their location may work just fine (like the scorpion).
Both also have a foundation in traditional magical practices, so it's not just munchkinry but trying to model real occult beliefs. That being said, I do see your points on how this may expand things too much and allow for rampant abuse if it isn't just something unique and tricky.
If used by the PCs....mainly I really don't see how it makes it much easier than the standard methods of getting a connection. A haircut mugging is simple but effective. The footpath method is too hard to actually get to work in a modern city, and could be prone to rapid decay due to wind, rain, or other people walking by if you don't collect the sample immediately.
The spell target method is absurdly high risk, and can be foiled by the target simply dropping it or changing clothes. They don't even have to do this on purpose. There's also precedent, since aside from the scorpion, Harry used a bit of his own hair attached to a fake Sword in order to track down the person who stole it in The Warrior. It worked pretty well, though the guy ditched the sword.
Besides, if my players continue their current record with investigations and trusting the villain, I'm afraid handing them a bag full of his clippings is just about the only way they'll figure it out. If they survive the bees. (My god.)