Do you mean as threats or in a conflict? In the case of the former, I think Brainiac has the potential to be much more than "just" a Superman villain. Convergence (as weak as it was overall) established this. The pre-Flashpoint Brainiac finding Vanishing Point and then accessing past timelines and Earths so that he can bottle portions of them before continuity changes is a tremendous threat. Even Darkseid hasn't done anything on this scale, at least nothing I know of. I think the next logical evolution would be to see Brainiac bottling entire universes and becoming a Borg-like threat on a multiversal scale. He isn't interested in conquest but he is (sorry Larfleeze!) the ultimate collector.
That would be quite the match up. I'm surprised it hasn't been done yet.
I feel that it's fair to blame IP owners for being creatively stunted but that it's also fair to blame the audience. The general audience doesn't seem to have a problem with "more of the same," which is why I think we're stuck where we are in various genres and media today. Even George Lucas was intent on returning to Darth Maul in his plans for the sequels despite his original idea seeming to involve an immortal and body-hopping Darth Plagueis. Lucas more than anyone has learned just how stubborn some fans can be.
Agreed. He's more interesting as fodder for big battles, whereas Darkseid threatens much more than just the body.