Coaches do have quite a large impact on teams, they're the ones who study the opponent, formulate strategies, and then translate that into a training regimen.

In so far as being a kid is playing sportsball the coach is primarily the genome, then with some distance culture (takes a village and everything), and then the parents. You can praise a parent for having the wherewithal to introduce their kid to spaced repetition software, you can't praise them for the kid feeling inclined to learn six languages before the age of 14 that was all the genome spotting a niche, adapting a suitable individual to serve a role by making it excited.