This is a common claim as to why Bargnani's defense isn't as bad as it appears. Unfortunately it doesn't hold water. First of all, Amir is a very good team defender, despite the shortcomings of the team. Also, Bargnani's problems have nothing to do with anyone else. You just have to watch him on the court to see that. He really doesn't seem to have a clue of when to rotate and where to go when he does rotate. I've never seen a big man make so many bad decisions playing team defense before. Even in the Boston game, which was supposedly a good game for him, I constantly saw Bargnani not rotate when he was supposed to, not rotate hard enough when he did, etc countless times. And I wasn't even looking for it.
And Bargnani's man-to-man defense is often vastly overrated. He defends well against a very specific type of offensive player some of the time. He struggles most of the time he has to move his feet or make decisions on defense.
Even JoePanini, who is a Bargnani fan, admits that Bargnani is a very poor defensive player.