I disagree that rating is the sole determinant as to whether one can be a competent coach. I also disagree that it is not possible to be an effective coach for someone having a higher rating. Indeed, in many sports (e.g., tennis), coaches of the very top players cannot beat their students. However, this does not mean they cannot help their students improve. Often, the best coaches were not the best players at the sport or game that they coach. Being able to evaluate a student's weaknesses, understanding how to develop training regimens personalized for particular students and communicating/explaining concepts well are attributes of a good coach/teacher. Top players do not necessarily have these traits.
That may be true in physical sports, but not brain games.
lol