The point is that even in the NFL, there's a wide and very visible gap between the top and bottom levels of quarterback play, and that's taking into account that these players (including the backups) are already considered the best of the best.

I only mentioned the NFL because I was riffing on your comment about throwing footballs, but agree that it's generally a stretched analogy. The extreme scarcity at the top of most professional sports and the resulting lack of utility/career viability outside of the big leagues doesn't compare well to most vocations.

The argument also assumes the only reason someone plays football is to play in the NFL. I invested significant time learning to skate because I enjoy it, not because I think I'll become a professional hockey player.