The only thing is his number great coaches 1- 1000. Probably more like 1-100. I in fifty being really good, 1 on 15 being good, and 1 of 2, passable.
Baseball a game of statistics this is just another one, part of the reality they face trying to play ball.
The odds of being a great baseball coach are pretty low, kinda like being a Great baseball player, it just a hard thing to achieve.