&gt;imagine a soccer team where 20% of the players are swimmers, 30% are basketball players and the rest are gamers. 

This metaphor doesn't work at all. Society doesn't have one goal the way a soccer team does, which is winning, and also doesn't need to specialized. Everyone in Japan and China doesn't specialize in one thing, the way soccer players would on your metaphor. And diversity in films and things like that is because there already is a diverse society in places like america, and filmakers are trying to appeal to that audience. They might go overboard but that doesn't mean diversity is wrong.