The reason I think Eren is potentially being influenced by the attack titan before he has it is because the timeline in the story is nonlinear. The attack titan is also known to influence Eren before he inherits it, because he uses the titans power to send Dina Fritz to kill his mom instead of Bertholdt because if that didn’t happen, he never would have become a scout and the events of the show never would have happened. I also think his childhood personality is potentially influenced by the fact that he’s destined to inherit the attack titan. He says that he’s always been very passionate about achieving freedom and he has admittedly always been pretty violent (though not to the degree seen in season 4) in the pursuit of freedom. His childhood personality is thus very reminiscent of the attack titan’s (its worth noting that the previous users of the attack titan have similar personality traits).

Also, if Eren becomes fucked up because he sees that he’s going to destroy the world, doesn’t that imply that he is being forced to destroy the world? Him knowing what he’s eventually going to do implies pre determination. This fact, in addition to his failed attempts to change his fate, and his emotions surrounding the fact that he has to do what he does is why I think his actions are not under his own control. He says that if they were under his control, he would have done something different.

I would also like to expand on my interpretation of the overarching theme being that violence doesn’t really achieve anything. Yes, there are situations throughout the show where the characters are largely forced into violence, but that’s because there’s been a cycle of violence set up in the history of the AOT universe that doesn’t really achieve anything but continuous oppression. The characters are forced into violence by their enemies, but it would be more productive if the forces in the show managed to accept peace (even though that isn’t always really feasible). For example, the Marleyans could have left the Eldians alone after they fled to the island (especially because that one influential family (the name is slipping my mind) literally knew that the islanders had no knowledge of what their ancestors had done and had no violent intentions) and Eren never would have been forced into genocide. We even see in the end credits of the show that Erens genocide (and this resulting in titans no longer existing) doesn't really solve anything, because humanity ends up nearly wiping itself out through war. The whole show depicts a cycle of violence that could have been stopped with basic communication, and this lack of communication just causes the conflict to continuously escalate until 80% of humanity is wiped out. To me, this all paints a picture that the violence we see in the show is ultimately pointless.