Not playing the position isn't a very legitimate criticism if one considers which coaches have taught what. First, consider the alternative, that playing the spot or even sport makes one better at teaching it. Are the best players in a sport the best teachers of it?
How many high powered golf teachers never made the tour? Would Mike Jordan be a good coach? It isn't playing, its the ability to teach sports movement and tactics. Those abilities are inherent, and while certainly the familiarity with a particular activity lends to depth of understanding, that doesn't preclude acquiring that body of knowledge as an observer.
How does one become an OC or DC without having played all the positions they now command? Many serve in a variety of position roles to satisfy that very acquisition of acumen, although they didn't play all those.
Good coaches are born to it, and they don't much care what it is they are to teach in terms of ability to do so or not.
But! If we are going to denigrate a coach for not having played the position in their charge, how do we give any creedence to an assessment of a coach when the fan has never played the position or themselves coached? If a coach can't gain the knowledge while immersed in the role 24/7, how does the fan gain enough info to know the coach hasn't?