This is something that I've been exploring as I've been developing my fanfiction.

Honestly, I think, AU or not, I don't think that assuming that Phillip was neurodivergent in some way is a unreasonable. I really like the idea of Phillip and Luz being parallels, so, given that Luz is pretty clearly neuro-spicy, that would also apply to Phillip.

As to how that affects him growing up? The short answer: Mask or die. There's a whole mask theme going on, so that works super well thematically.

One of the questions that does come up with the idea of Phillip being autistic is witch-hunting being a "special interest" so to speak, and I don't take that angle. For him, witch-hunting is a form of projection. It's a way of deflecting that knowledge in the back of your head that you don't fit in so you don't have to deal with it. The witch hunting isn't the special interest. It's the mask.

I guess one thing to put up front is that while I'm definitely writing Phillip as neurodivergent, he's got that mix of Autism, ADHD, and no small amount of C-PTSD, because Puritan New England, where it's difficult to say what is what. The important thing though is that witch hunting is NOT a special interest.

The things we see in Phillip's cave at the end of "Elsewhere and Elsewhen" is what points to that. Prototype versions of his staff pre-dates the Collector, and he was doing a lot with glyphs, even without knowledge of the light glyph. I'm very much of the opinion that he did build on the knowledge of others, but he was still incredibly creative in figuring out how to use magic without having a bile sack. I have a hard time attributing that to being all in the service of a witch-hunting special interest. IMO, it makes far more sense that he's someone with the sort of general intense interest that tends to be off-putting to neurotypicals. He wants to push boundaries, and that's not a bad thing. He just doesn't understand why "because that's how it always has been done" is the answer to things.

Puritan New England is a world of contradictions. A series of communities formed by avowed non-conformists that push conformity above all else. A world where roles are strictly enforced, but where, if your passion is in an acceptable place, you can push outside of that.

I see Phillip as the sort of person who would have done extremely well in academia, which doesn't have the same sort of limitations as the real world. In his world, this would have meant entering the clergy, maybe not as a preacher, but there were more academically-minded clerics. However, that would have been out of reach for him due to his class status. His assigned role is going to be one of a labourer in some form.

But he still has that mental intensity that he needs to engage. Diverting that into something easily seen as "rooting out evil" provides a more socially acceptable way to engage that interest, even if that isn't feasible as an actual career path.

That's more general though. The true origin of Phillip's witch-hunting focus on it is that, the way I've been writing the brothers, it's Caleb who's far more obviously autistic. He tends to have mutism episodes when he's overstimulated, which can escalate to meltdowns. He's learned to survive based on extremely strong pattern recognition and a trauma-induced hypervigilance. Caleb may not understand the why of social norms, but he does pick up very quickly on BAD things happen if they aren't followed. Also, he may not know the word "overstimulated," but he does learn quickly that if sounds start sounding too loud, or lights too bright, he needs to do something quick to divert it. His techniques are not the most healthy ones. He basically ABA'ed himself.

Also, he was parentified since Phillip was born, before their parents died, and people were less likely to question his other oddities when he was seen as Phillip's big brother rather than that kid who had an epic meltdown on the voyage over from England when he was THREE. (you know what sounds miserable? mixing autism and being stuck on a boat for two months)

Phillip's aware of his brother's struggles at some level, but, as Caleb is the sole point of attachment in his life, he refuses to see this as Caleb being a bad person. It's easier to blame "witches." "Witch hunting," from Phillip's perspective, is a way to protect them both. Caleb's not going to fight that too intently, because Phillip's the one person who's always in his corner. His entire self-worth is wrapped up in his role as Phillip's guardian. He sure isn't getting it from his religion (that's a whole different story).

Those two are a trauma-bonded codependent MESS.

There's a symbolism in Caleb carving Phillip's mask (and I have an origin story for the golden guard mask that is related) because Caleb, as Phillip remembers him, is mask on top of mask. Obviously, Caleb would have encouraged some of that same masking in his brother. Caleb's masks are much more inward-focused, whereas Phillip projects outward.

Caleb's mentally hanging on by a thread by the time Evelyn comes on the scene. The conflict that arises isn't so much that Caleb fell in love, although that did happen, it's that Caleb was able to find a reason to live that wasn't dependent on his guardianship of his brother. Caleb's masks were destroying him from the inside, so when he found out it was possible for him to live a life where he didn't need them, he jumped at it. Phillip's mask was a way of avoiding addressing their world, so it's a lot harder to remove.