I think it needed an extra ten minutes at the end of the movie that showed a traditional Joker heist. Two reasons. One) this movie was building up to the "birth" of the Joker, but we never get to see him do anything. It would be like ending a Spider-Man origin story right after catching Uncle Ben's killer. Two) the movie could have benefited from showing how truly monstrous the Joker really is. Besides the one woman, he didn't kill anyone other than who he had been personally wronged by. Showing him be truly evil and avoiding Gotham PD would have driven home that he was an iredeemable monster, not just a broken man.
imo that would be anti-climatic though. I think it made sense to end with the riots and the elevation of Joker to a symbol, along with the murder of Thomas and Martha Wayne.
additionally, that one woman he kills that didn't wrong him does indeed happen at the end, so you could say the end *does* end with his final transformation into an irredeemable monster ---
A very happy young man looking forward to a bright and wonderful future.