Poker isn't like real sports. While there may be plenty of genius football or golf coaches that never reached the elite level as a player, only the elite players themselves can write the best poker books and provide the best training videos. It's not really possible to be a mediocre, or losing poker player, but also be an elite poker coach.
You could be a great mental coach, preparing someone to be the best player they can be without also being a poker player, but that's because the coach isn't required to know what to do with AQ under the gun.