Clubhead speed represents mostly momentum transferred from the body to the clubhead. That's why the hands have to be loose and freely pivoting. Body momentum needs to be downward and around. Hip rotation, arms pulling downward and the squat all direct body mass down toward the ball. The clubhead lags behind a bit, and then at some point, it begins its very rapid acceleration around the hands toward the ball. At the point of impact, all those moving high-mass body parts are very nearly motionless -- the clubhead is actually pulling the hands/arms around at that point. The momentum of the dropping, twisting body is transferred to the clubhead at impact.
So, I think the squat isn't so much about needing extra flex or pre-flex in the legs as it is about adding momentum and power to the downswing. It's pretty tricky to time this move. Not many people can pull it off. Sean Fister hits the ball pretty far without that squat!
BTW -- the best baseball hitters don't squat as they swing. They just turn from their launch position.