But that's only comics. And only because DC hasn't really figured out how to sell Joker and Harley to the comic book readers. Imagine if they ever get an ongoing series with top tier talent.
For the general audience, those two are a much bigger deal than Superman. Look at the Joker movie making billion dollars at the box office, or Harley Quinn's cartoon being so wildly successful. Superman's recent movies and cartoons have not been anywhere close to them.