He still is but it used to be a clear gap, now there isn't one.
Anthony Davis and Demarcus Cousins are coming for that crown. Al Jefferson can lay claim to being the best center in the league. Tim Duncan at his best is probably still the best C in the league, but he can't maintain that all game/season long. Marc Gasol would probably be able to call himself the best but he simply isn't aggressive enough. Joakim Noah isn't Howard's level but he puts tremendous impact on the game. Marcin Gortat is great in spurts.