I'm gonna offer a counter-argument. It's one you've seen before, I suspect; but maybe a few details will be new ...
WoJ is that there is enough evidence given in DB for a reader to ferret out Cowl’s identity.
Upon a reread of Dead Beat, I caught onto a few more hints that lead me to believe that Simon is indeed Cowl. It’s still possible that Justin is Cowl, but I find that to be increasingly less likely.
#1
Bob’s behavior in DB has always been odd to me.
In Chapter 3 when Harry is asking Bob to remember his time with Kemmler, Bob says that he can’t because he either chose to forget, or was compelled to. The only owner Bob had between Kemmler & Harry was Justin - if Justin was indeed a Kemmlerite/ student at some point, why would he compel Bob to forget his memories of his time with Kemmler?
Being that Bob is a being of knowledge without morality, I find his choosing to basically amputate his own arm (Bob’s textual metaphor) to be highly improbable. Instead it makes more sense that Justin had a similar experience to Harry when he questioned Bob about Kemmler (Bob tried to kill him with the blue light thing) so Justin forced the spirit to forget that part of his life.
#2
Justin would’ve owned Bob for ~30 years between Kemmler’s last stand in 1961 & when Harry takes him from Justin around 1989-90 (10ish years before Stormfront).
When Cowl sets Bob down by Harry right as he’s about to perform the Darkhallow, Bob is able to revert to becoming Harry’s again - this is ultimately what leads to Cowl’s downfall. Bob is able to get into Sue, save Harry from Kumori which allows Harry to smack Cowl as hard as he can with his staff, thereby ending the necromancer’s chances. I don’t see Justin making such a rookie mistake with Bob - it seems more likely that someone like Simon, who never actually possessed the skull, didn’t fully understand how Bob’s loyalties worked & paid the price ...
I counter-WAG:
Cowl is Harry; Time-Travelling Harry.
You know how Jim has a
Mirror Mirror novel coming (that's got a bunch of explicit nods to the Star Trek TOS episode of the same name)?
You know how there's a bunch of time-travel episodes of Star Trek?
You know how Jim has more or less stated that he plans for Harry to break
every. single. law. of. magic. before he finishes the stories... so we know TT-Harry is coming?
I'm gonna point to the ST:DS9 episode,
Trials and Tribble-ations, where the DS9 crew goes back in time and runs around the edges of the ST:TOS episode
The Trouble with Tribbles.
So I'm proposing the TT-Harry novel is basically a Cowl-POV novel (recalling that Cowl
IS Harry -- Harry dressing up in a "Darth Wannabe" costume, running around being ominous and threatening... cosplaying a Bad Guy) recap of "what was
really going on" of all the bits of prior DF novels that featured Cowl... just like the DS9 episode was a BTS "really going on" of the TOS episode.
Possibly also things like the "mysterious repair" of Little Chicago. Either pop in thru Lea's garden, or just open the Wards he knows how to open & walk in the front door. Cue amusing byplay with Bob -
"Uhhh... Harry? What happened to you?"
"Holy Crap! You broke the Sixth Law??? Cool! So are we going Warlock now?"
But this is a sideline to the Cowl thing...
#1
Bob’s behavior in DB has always been odd to me ...
That's because Bob was obeying Harry',
and obeying Cowl'ed Harry. Cowl had (I wag) given explicit and strict directions to Bob not to
ever hint/show/acknowledge to Harry' that Cowl=Harry. The only way Bob could have clued in Harry' is if Harry' had asked some specific and explicit questions, putting Bob on the spot in ways that Bob couldn't hide that he was trying to hide something (and Harry' would have had to have some pretty sharp suspicions).
...
#2 ... When Cowl sets Bob down by Harry right as he’s about to perform the Darkhallow, Bob is able to revert to becoming Harry’s again - this is ultimately what leads to Cowl’s downfall.
... it seems more likely that someone like Simon, who never actually possessed the skull, didn’t fully understand how Bob’s loyalties worked & paid the price ...
When Harry' managed to "break through" to Orange-eyed Bob, that was just a light-show,
literally. Bob was never obeying anyone
but Harry. Harry' knew that EvilBob had blue eyes and talked in a factual, "yes Master" manner, so CowlHarry instructed Bob to put on his Bad Boy drag accordingly. Bob would have loved it!
Cowl knew what was coming,
he'd already lived it. Harry's staff-strike was a normal, muscle-powered blow; enCowl'ed Harry could easily have crafted a micro-shield item/potion/etc that would have softened the strike to a mere love-pat. Hell, if Cowl-Harry was still WinterKnightHarry (and I'm pretty sure he was, if my WAG is right) then he might even have been able to soak the whole thing with the WK-Mantle.
You remember that scene in DB where Harry "duels" Cowl? Cowl hits Harry with a force-strike very-much like one Harry (a much stronger Harry) might toss. Harry uses Hellfire to boost his return-punch, and throws a car on top of Cowl.
There was the sound of metal grating on concrete.
"Oh, come on," I said, panting.
The car shuddered, and slid a few inches to one side.
Ya know what that sounds like? That sounds
exactly like a Winter-Knight Mantle in action, is what
that sounds like. Maybe a shield-spell to help soften the impact. But then raw WK strength, for just a moment.
===
There is a key bit of theorycrafting I haven't seen before: Cowl was known to all the other Kemmlerites. So Cowl
cannot be Harry...
Or
can he???!?
I don't THINK this theory goes so far as to have "TT-Harry" go back to Kemmler's lifetime, and become a fake apprentice for YEARS (just so he could be the person doing the Darkhallow as a sham for Harry' to disrupt).
I mean... maybe? It'd be kind of a Snape-and-Voldemort-as-seen-in-the-Pensieve sort of thing, secretly-good-Harry apprenticed to Voldemort-I-mean-Kemmler. But we know Jim isn't above making that kind of nod to pop-culture, and he has mentioned the Other Wizarding Harry a few times... so, maybe?
But instead, I'll draw upon another of my WAG's -- that Harry has a "natural gift" for necromancy; that it's actually one of his strongest talents! See here:
https://www.paranetonline.com/index.php/topic,53380.msg2326335.html#msg2326335So I'm going to suggest that future Harry ambushes Cowl, swipes enough of his memories (mind magic) and just hides being Harry inside his ... cowl. Jim has given several strong statements about Cowl and who-is-Cowl, about wizards and secrets and needing to hide identities. Can't you just SEE him chortling inside as he thinks how "the people Cowl
really needs to hide his identity from" are...
the other Kemmlerites? Harry just fills in the rest with "natural talent" (born necromancer, yo!) and the knowledge he got from reading the Word of Kemmler (and maybe other bits of Lash/Bonnie info, and/or other stuff that he learns between SG and when he TimeTravels).
If Kumori is Molly, the mind-magic is a gimme. Molly's too short, but (a) we know fae grow in stature as they grow in power (that even happened to
Mab, way-back-when!), so TT-WinterLadyMolly could easily be a bit taller & (b) Jim has stated that shapeshifting is just another spell, so either Harry OR Molly could probably craft a "get taller for a while" potion without much difficulty.
Or Jim could just say (via author-fiat) that Harry has learned enough to be able to do the mental wonkery on his own.
...#3
When Cowl ambushes Harry at Murphy’s house right after Harry calls up the Erlking, he tells Harry about the wardens being in the city. Seeing as the wardens has arrived in Chicago the previous evening, I find it interesting that Cowl knew of this a few hours later ...
CowlHarry obviously knew everything Harry' knew. But I bet CowlHarry didn't remember all the exact details of the timing, the o'clock timepoints where person-A would be at location-Alpha.
I think Cowl had independent means of checking on this -- CowlHarry obviously also had Toot, to surveil the shit out of everything he wanted ... and he knew more about everything that was going on than Harry knew ... And I bet CowlHarry had a BUNCH of extra Nevernever resources, and could do a very-comparable Nevernever-side surveillance of -- e.g. -- the White Council travelling via the Ways.
WoJ is that there is enough evidence given in DB for a reader to ferret out Cowl’s identity ...
I will be so bold as to suggest that, in fact, all your lines of argument are
stronger as arguments for "Cowl is TT-Harry" than they are for Simon.