I had that argument with a coach that will remain unnamed. He seemed to think that if NFL was to suddenly switch to rugby that they would absolutely dominate the rugby world. The only point that is valid is that it is a larger population base to draw athletes from. Everything else is moot as you just won't get a guy that is the size of an NFL player to keep moving all game with no substitutions and breaks. Just as you won't have key players covering a half marathon every game unless they are lighter like the AFL guys. So all the athletes have trained and developed to suit the game they play.