Props to Bisping to counter wrestling Sonnen, but Sonnen has almost zero submission plans. Although pupil means only student, when said in Portuguese normally means a well regarded student and that is an understatement about Vitor and his Master. Vitor is not a wrestler, he is a BJJ black belt and I believe it's not quite fair to judge nobody defense/activity while having Jon Jones in his guard.
To survive for almost four full rounds playing around in Jones' guard is an achievement in itself. How long have other fighters lasted once Jon scored a take down. Jon Jones has the most dangerous and ruthless top game in the entire sport right now. For Vitor to last so long on the ground with Jones on top and neutralise most of his attacks whilst almost securing an arm bar early on his extremely impressive.
Vitors grappling game I feel is being vastly under rated here, like you said, I think he's a much better over all grappler than Bisping and Mike has never really had a good offensive wrestling game. His defensive wrestling is definitely solid, but his offensive game and take downs leave a lot to be desired. Any one remember the take down he tried to get on Dan Henderson, and Hendo just looked at him and laughed.
Vitor is the much more dangerous striker and over all the more technical one, and is the over all superior grappler. Bisping has the edge in cardio and pace, but I don't think that's going to be enough to secure a win.
Belfort should KO Bisping within two.