For example, they have something like four pitchers on their team, but he keeps having the same one throw pretty much every game.

I know nothing about this particular coach of course, but it was my experience growing up that most coaches of youth sports in USA don't have much idea of what the hell they are doing. I had a soccer coach that would bring the equivalent of "coaching soccer for dummies" to the practice field each day because he was a math teacher looking for some extra money after hours, had never played soccer, and certainly didn't have any coaching experience. For me, if I wanted a higher level of coaching standard, I had to join a private league that was called AAU. I'm pretty sure it, or something like it, still exists. Perhaps your niece could look into this.