If I'm better that the instructor what good is the instructor in teaching me?
ask Payton Manning why he has a QB coach. or ask why the QB coach isn't starting instead. same answer.
the real key is as was recently described in another thread, the difference in training and practice. training requires someone to watch you because you really can't see what you're doing wrong in many cases. it takes an outside perspective, even if that person is not as skilled.
often, different backgrounds help a lot. i remember working on movement when i was shooting 3gun and then taking a carbine class from a well regarded trainer who taught how to turn. i was thinking "you could save a half second by..." when he started explaining (roughly paraphrased) "when there's blood on the floor, keeping your CoG over your feet will prevent you from assing yourself." apparently, blood is slippery. i wouldn't know.