Do coaches of Olympic athletes have to be better at that sport than the people they are coaching?

I was brought to this question by thinking about how some esports teams have coaches, but what are they gonna show them about the game that they don't already know? Hungrybox has Captain Crunch, but there's no way Captain Crunch sees something that hbox doesn't. How is an Olympic coach going to help the best diver in the world get better at diving?