BJ has an incredible amount of natural talent, and his awards speak for themselves concerning his technique. On the other hand, it just doesn't seem like he trains to the level of some of the other champions. I'm a huge fan of Penn. In fact, I'd go so far as to say Penn's my favorite fighter. I like the guy's attitude of "just scrap."
On the other hand, if you're going to come in against a red hot GSP, or a ultra-trained Matt Hughes on the road to redemption, you better be in the best shape of your life. You have to have outstanding cardio and pack as much muscle onto a 170 pound frame as you can. BJ, for all his impressive talents, rarely comes into a fight cut and hungry. If BJ trained at the level of a Hughes/GSP style fighter, I think he would truly be unstoppable.
But wasn't it Penn who said training like that "bored" him and burnt him out?