Joker: Fantasy and Canon

Checking in with a late review of Joker (2019), which the wife and I saw on HBO last night.

Let me stipulate several things:

• Joaquin Phoenix was brilliant, inspired, incandescent, whatever superlatives you can find, in the title role.  He eminently deserved the Oscar he won for that.
• I know a middling amount of Batman canon, but am no expert.
• I thought the movie held together very well as movie, which means I disagree with, for example, the inanely critical review in the New York Times, as I often do.

I do have question about the ending, though.  And the fact that I have questions makes me think that maybe the movie would have been better ending before this ending.

Arthur Fleck, having actualized his impulses and become the Joker, is seen talking to his state-appointed shrink or social worker, but in a less dingy setting than at the beginning of the movie.  One explanation of this scene, which I'd like to think is correct, is that Fleck, after escaping the cops in what I was wish was the closing scene, is nonetheless apprehended at some time in the future, and is now in some kind of penitentiary serving a life sentence for his crimes (or is he maybe on death row?).

But there's an alternate explanation (which my wife wondered about, and now I'm thinking about it too).  We already saw, in the movie, that Fleck imagined making love and all the good things he did with his neighbor down the hall, Sophie.  This establishes that Fleck's fantasies played a major part in the narrative we see on the screen.  Is it possible that everything else we saw in the movie - Fleck's killing of De Niro's Murray Franklin (who, to me, is just as much Joe Franklin - believe it or not, I was once on his show, talking about my album, Twice Upon A Rhyme - as Murray is Johnny Carson), etc - were also just in Fleck's mind?   Or, at least more of the major sequences than just Sophie as girlfriend?

In at least one Batman movie, if memory serves, the Joker kills Bruce Wayne's parents.  In Joker, one of the myriad angry people with a clown face does the deed.   This suggests that Fleck did not make all of this up - another clown killing Bruce Wayne's parents is consistent with the historical Batman canon of his parents being killed.

In any case, I rate this movie as maybe a masterpiece, and, the more I think about it, the more I think that's right.