Eren, the kid who killed two men with a knife tied to a broomstick, has always had issues.
I think he is definitely naturally like that. Before he even inherits the AT and FT, we see him go all hotheaded on Hannes in episode 1 for not taking the titans seriously, we see him calling humanity weak and like cattle with nothing to live for.
again, with the way the attack titan works
that could be OLD eren, influencing kid Eren
I get what Gustaf is saying.
Eren was clearly experiencing future visions even before he officially got the Attack Titan. It's very possible that Eren's personality from birth was being influenced by an older Eren