If you define "player" in this context as "person who bought the game and opened it at least once" then becoming top 90% in any given game really doesn't take much. If Steam achievements are accurate just playing the game for an hour will make you above average. Most people quit before that and thus have no time to learn the game.

I still agree with your last paragraph. In gaming as in professional life, a T-shaped skillset is really useful. Having broad knowledge and experience, even if it's mostly shallow, is incredibly useful.