Its an interesting observation, plenty of struggling back pocket/flanks make exceptional coaches. But generalistations can be problematic.This might be more compelling if after several years spent learning the craft from nicnat at training our young rucks weren't absolutely trash.
Its a huge generalisation, but often superstar calibre players whose game relies on freakish natural ability (and nic nat is about the best example of that I can think of) are no good as coaches- because the things that made them good players are effectively unteachable.