It isn't the kid who is starting on the bad team that is getting pushed out. It is the kid at the end of the bench on a bad team who is getting pushed out. How could you possibly define that kid as talented?

And to answer your question, no it isn't the purpose of school. Sports in general aren't the purpose of school. But since schools do sponsor sports, and they are an important part of adolescence, I would accommodate kids in their pursuit of simply being able to participate. And I would say the same thing for a kid in dance, music, art, etc. If you have a passion for it and are talented enough to participate elsewhere, you should be given that opportunity.