My old uncle once told me" if you cant do it it- teach it. I can teach you how to to trade but it will cost you £3k for a super duper course- any takers? And no I am not Arthur Daley...
In the musical world, some of the greatest teachers were formerly great performers. My point is this: I believe in order to teach well it isn't necessary that you perform well, but it is necessary that you did at one time perform well.
Not necessarily, great athletes rarely become great coaches eg best football coach ever Bill Walsh never made it to NFL as a player, best soccer coach ever Jose Mourinho never made it to the top tier as a player. Do you think Bobby Fischer would have made a good chess coach?