And I suspect he hasn't tried to take the tension out of his shoulders, which is a simple thing to do, and you don't know that it wouldn't help. Taking tension out of the shoulders is not the same as telling him not to shrug.
Shoulder tension is one of the most overlooked swing wreckers, and even if eliminating it doesn't eliminate the shrugging, it's still a plus.
Good grief, I didn't say to tense up for the rest of his life. I said use it as a tool to limit, learn and loosen up. You read the word 'tension' and went on a tangent.