I’ve just realized what bugs me the most when I’m comparing canon and fanon Martin. It’s the fact that in canon he never really changed.
I’ve said this before, but right now it really hit me. The Martin we see in early seasons is exactly the same Martin we see in season 5. He had always been like this.
I feel like the reason people talk about his “change” in season 5 is because up to that moment we’ve mainly heard Martin interacting with Jon, the man he had a crush on. Of course he’s gonna be stuttering and awkward! But when talking with Tim for example, Martin is his usual self - unless Jon is mentioned, of course.
Also there was this whole thing with the Lonely, where he got depressed and isolated himself from everyone. But for some reason it wasn’t a catalyst for his character development - when he got out of it, when he got out of the Lonely, he stayed the same as before. He just gained some self-awareness.
Season 5 Martin acts this way because at that point he has an idea of what’s happening and isn’t so anxious about his surroundings anymore, and, like every person that’s not being absolutely crushed by guilt at that time (Jon), his main objective is to get revenge for all the suffering he had to go through. Every other person from the archive crew would’ve done the same if they were in his position.
And there’s also the matter of him falling out of love with Jon / starting to see him more as a weapon, a monster, or just “his boyfriend” rather than a person.