If you put a half decent kickboxer in Leben's fights, they all would have been KOs. Leben had plenty of opportunities to KO Cote and he didn't. Leben had a dozen opportunities to KO Fioravanti and he didn't. He got lucky that he won those fights in a decision.
Leben has proved, twice in the UFC and probably much more in the rest of his carreer, that his kicks are poorly executed and his punches are badly timed or very slow. He has endurance, that's all. If he gets a title fight he'll miss too many punches and be destroyed. If he fights a guy with a good groundnpound (of whom there are none in the middleweight division) he'll be runover.
People get blinded by his hair and bad boy mouth and so they cheer for him without looking at his stance, strikes or groundwork. He is not Tito Ortiz or Cabbage. He doesn't have a chance with a real hardstriker.