A lot of coaches are great at filling out a line up, but when it comes to developing talent, not so much. And that's because it's not easy, and the pay off isn't immediate, whereas, like SomeBaseballDad noted, "If a player doesn't perform right away it's on to the next player."
There are coaches in high places that have stumbled across great talent, and they're touted as great because of the association with the player being there. However, and I mean this with all due respect, the great players are going to be great, regardless of most coaches. Having a great player does not mean the coach is also great. How is the development of the middle and lower tier of the line up?
With regards to the OP, I've nothing substantial to add that others haven't already said.