I get that it's fun to think about Burt as a deranged psychotic pedophile rapist but I really don't see that being the case. He's obviously mega autistic and doesn't know how to act around people, which explains the general aura of fakeness and the weird rehearsed mannerisms (I feel like he's spent a considerable amount of time in front of a mirror trying to get the snap-wink-hump-smile -combo just right). Rather than being himself, he finds it easier to make up a character and the more extreme the character, the easier it is for him to play.
You could see that the prison rapist character was easy for him, not because he's a rapist but because he knows exactly how to act: Kubrick stare, lick your lips, talk about raping people. The more one-dimensional the character is, the better he is at portraying it. That's probably why he became Dark Burt, TTS told him he'd have to do shitty things to win, and he doesn't know how to be shitty unless he's playing a shitty character. As Dark Burt, there's no internal conflict, he can just think "what would Dark Burt do?" and do that.
Even Burt is a character, obviously there's a lot of him in it but I have no idea (and I don't know if he has either) what the "real" Albert Appouh is like.