Who was more popular in the Austin Powers movies, Austin or Dr. Evil? They spent as much time in the villain's lair as they did following the hero, and audiences ate it up. Look at Hannibal Lecter. Look at Groo from Despicable Me. Most mob movies, including GoodFellas, The Godfather, and Casino. Res Dogs, Natural Born Killers, Maleficent, The Usual Suspects, A Clockwork Orange, Ocean's, The Devil's Rejects, The Vampire Lestat, American Psycho, or just plain Psycho. Most of critically-acclaimed TV nowadays is told from the POV of the villain(s) --- Breaking Bad, The Sopranos, Sons of Anarchy, Boardwalk Empire, Deadwood, The Borgias, Hannibal, Dexter......
I don't think a movie about supervillains would have any trouble finding an audience at all.