controversial opinion but I think s5 Martin being the human is a bad writing choice, especially since he is very much s3 Jon in terms of being an avatar and people were already treating Jon as a monster back then
I believe the reason why it happened is that they accidentally wrote themselves into a corner regarding Martin's character. he changed during s4, was pushed further into his own head and loneliness, made less human by Peter Lukas. but he also has to stay as he was before s4 for him to be Jon's rock/human boyfriend who is his moral compass. Martin was able to vanish, he has a domain. he is as much of a monster as Jon was in s3. however, he also has to be the human one, the moral one. and it just doesn't work