You know, I think that that idea of personality comes the closest with me, as well as the caveat that people might not have one True Personality, but behave situationally and can almost become different people based on what situation and environment they're in.

So I agree with you that I don't like at all stories where backstory is arbitrarily changed or added to, especially if the writer is going to introduce a Major Traumatic incident which is secretly the golden key to the entirety of the character's actions.

As for AUs, well, I just don't like them because I have a love-hate relationship with worldbuilding, and a lot of the times the world is like a character, and I think you gotta include it.