"Sure. Mozart had an impact. Then he died when he was thirty five. We'll never know if he was really any good because we'll never know whether the stuff he would have produced when he was fifty or sixty would be just as good."

Ugh, chances are, you definitely have no idea what you're talking about.
Considering Mozart, I'm assuming you're talking about W.A. Mozart, composed OVER 600 COMPOSITIONS

http://en.wikipedia.org/wiki/Wolfgang_Amadeus_Moza rt

I'm pretty sure people who know what they're talking about have a good idea of his compositional abilities.