If it is true, the sparring as a training tool in combat sports would be inefficient. However anybody knows that without sparring you can't learn how to fight efficiently...
So I believe the facts plays against your believes
Sparring in a combat sport is a totally different situation. In the OP's case, he's asked to practice a specific defense; in sparring, you defend (and attack) to exploit whatever situation arises, using whatever you think will work.