I dunno I liked the plot too. It’s a story about someone with mental illness discarded by society and driven to crime. Yeah some parts to do with Batman are weird but people rebelling against the elite and the rise of a villain who you can sort of sympathize with is decent. Combined with cinematic style and score I thought it was better than I’d expect from a comic book movie.
Discussion
The part about someone with mental illness discarded by society is great, but the people rebelling against the elite and the general "eat the rich" sentiment doesn't fit into the story and seems forced. It may have been better if it was entirely about a mentally ill person driven to crime, or entirely about people rebelling against the elite. And then they made Joker Batman's step-brother.
I think that was done just to demonstrate his rise to power and what may have made people follow him. It’s a Batman nemesis movie after all, even though the timeline doesn’t make sense.
But yeah, it could be a standalone movie about mental illness and crime but then it wouldn’t get the same level of marketing :)