Except for the sole black character in the film being the woman he desired and reacted violently to when he realized it hadn't happened.
Plus feeling victimized by everyone and that society itself is against you is wholly in the "Angry White Man" archetype.
Have we seen the same movie? Because that wasn't in the version of the movie I saw. Once he realized he was delusional, it cuts to him back in his apartment.
So it is left open whether he got violent or not. It's obvious how you interpreted that scene. I didn't, and thinking about it, I still don't.
Until he went to Arkham at the very end, he only got violent against people who were actually hurt him or threatened him. The three yuppie assholes, his mother, his co-worker who pushed that gun on him, Thomas Wayne, Robert DeNiro's character, ... he actually makes a point of not hurting his former co-worker who was never mean to him.
Based on that, and the realization being not that Sophie didn't like him anymore, but that their whole relationship was all in his own head, it is clear that she neither hurt nor threatened him. It therefore would be out-of-character if he actually had hurt her.
So, just like Arthur's relationship with Sophie was all in his head, him getting violent against her is all in yours.
Of yeah, now that you mention it she was also there...
...And also killed by Arthur because he resented her.
Lovely.
Two different characters. There's the therapist/social worker, played by Sharon Washington, who has a substantial role in the movie, and does, presumably, survive, and then there's the Arkham therapist, played by April Grace, who was only in the one scene at the very end, by which time he's in full Joker mode. That violence also happens off-screen, so whether he killed her or just injured her is unclear.
There was also the mother with her kid on the bus. And Chris Redd's character at the Comedy Club. There was also a black clown at the agency. Should I go on?