It seems to me that Kishi is setting up all of Sasukes battles to be sort of flukes, in other words you couldn't really attribute the win to Sasuke alone. On the other hand all of Naruto's fights are all won primarily through his own ability and determination. I don't think you can really say Sasuke is overpowered, and even if he is, he is still always blowing it and generally needs someone to help him mid fight. Without a tons of help Sasuke would have been long dead. (for example: Killerbee fight, Kage Summit)