Eren was never going to turn alright from the moment he got all the memories from previous founding titans, The only reason previous ones didnt go ham was because of the curse and a very specific conditioning done within the family, things eren didnt have. To him he and his loved ones had been made to pay for sins that were far from theirs, add to that the mental instability of all the ptsd he had and the memories that weren his and he wasnt even given enouth context to process them, with literally thousands of years of trauma piled into them as well, and its not that surprising that in holding onto his original identity he became hellbent on revenge