Just keep calling him Obito, I intend to. It's pretty ridiculous to change his name because he's a jinchuuriki now, I mean we don't call the star of the show Kyuuruto.
It has nothing to do with being smart or not. It has to do with emotions and having that little extra something to help overcome the Bijuu. In this case, Obito has gone so far down the path of darkness that there is nothing left that can fill the hole in his heart (even if he technically doesn't have one). Naruto has his mother and father and the memory of them. That's what filled his hole and allowed him to start taming and befriending Kurama. Obito - love + Juubi = Juubi taking over Obito and going on a rampage.
