I would much rather have a golf instructor who can hit the ball then one who cant. If a golf instructor cannot hit a golf ball essentially what he is telling me, subconsciously, I want you to do something I cannot do, I THINK I know how it should be done, but I cannot personally put my theories in action myself.
In basketball a coach does not need to know the mechanics of shooting so much, they have shooting coaches for that, he does not need to know HOW to box out, they have defense coaches for that, BUT he needs to be able to see when someone is not boxing out, and how the defense is breaking down, bad decisions on the court, etc... Head Football, basketball, baseball, soccer coaches are there to teach them strategy, assistant coaches deal with the individual skills
But in the golf swing you are not teaching strategy, you are teaching how to perform a skill. how much of a lesson is decision making skills, 10% at most, probably more like 1%, course management is easy to learn. The instructor should be able to demonstrate, instead of shank, thin, right, left. That is one thing that really impressed me with Brian and steve. They could talk for a half hour and not hit shots, then go and demonstrate and if they hit one bad one the next was good, but most all the shots were good. That alone makes me want to listen to them more, especially when they demonstrate different things and can swing the club multiple ways. If an instructor cannot do it how well do they really know their own method?