"Joker" didn't work for Joker (and neither did "Suicide Squad" or "Birds of Prey and the Fantabulous Emancipation of One Harley Quinn")! "Maleficent" didn't work for Maleficent! "Hannibal" didn't work for Hannibal! I cry foul!
Maleficent was the hero of Maleficent, not the villain. Suicide Squad should be an accepted answer for Joker, and I suppose technically Joker as well (though he's the protagonist and arguably an anti-hero, not a villain), but he wasn't in Birds of Prey.
I love that people love to say that it was written poorly and wasn't entertaining, but the main point of the movie is that we can still enjoy stories like them. It's a fun movie that wasn't obnoxious, let it be.