I think the best coaches are the ones who were below average players. They can understand the struggles of not having elite level talent and working through it.
I can't remember who it was but there was a guy who either played for Ted Williams or played with Ted Williams. Anyway, he said the reason Ted failed as a coach because he couldn't understand how to work with guys who weren't as talented as him. It was like a "I can do it, why can't you? It's easy". What's easy for Teddy Ballgame isn't easy for Johnny LessTalent.
I have heard that many times before, because the superstars usually made it based on some great natural talent and made it based off of this talent. The marginal guys usually had to bust their @sses off training and learning skills so they know what it takes to succeed more then just being born with a skill.
They also say too that usually certain position players make better coaches because of how they play the game. In Baseball, catchers usually make better coaches then say a pitcher because the catcher is usually the one studying the other teams and calling the games for the team and pitchers so they have to be smart and know the game well. They also get to watch the game from a totally different view/perspective then anyone else. In Football, career backup QBs often make better coaches then guys who were starters because they are often spending more time on the sidelines with coaches, going over things with them and the starters while watching the games from the sidelines.