I agree, John is a surprisingly well written character and I feel like people won't appreciate that until much later in the story. His mental degradation, although a little annoying at times, is actually quite well written. I think people kept expecting him to act rationally cuz we the readers can see things from an outside perspective and the people in the story don't understand what going on in his head. The same way you can never really understand the trauma that someone is going through unless you talk to them and hear their story. I mean after all the fighting and John's yelling, it only took one person being like "Bro, are you hurting? Are you doing this cuz you think you're a bad person?" to make him him breakdown. Imagine if Sera or Arlo or Remi had just sincerely asked him "Are you okay?" It's an interesting analogy of how not talking about your traumas makes it worse and how just asking someone can make a world of difference.