You're assuming that Braun's defensive inefficiencies start and end with errors committed. He had terrible reflexes, poor range, and just fielded the position awfully. It wasn't just the errors, it was also the balls he never touched. As many people as have mentioned it, I don't think it can be overstated. Braun was, literally, possibly the worst fielding third baseman in the modern history of the game. His defensive atrociousness almost wiped out his offensive contribution. For Braun to be a positive contributor if he plays third base, he would have to post a 1.000+ OPS, and honestly, I think that ship has sailed.