. Thats the sort of thing someone cant teach. Its instinct.
To a degree, yes, but a lot of it is about differences in technique. Sampras's quirky elbow-back swing doesn't requite as much of a unit turn as what they teach today or what Fed uses. Because he doesn't need it as much, he can continue to drive into the ball with his legs in between a closed and neutral stance. And because he has such explosive legs, well he can crush the ball when he's moving. Theoretically, linear weight transfer can generate more power than pure hip-torso rotation if you can do this at full speed. In practice, people do both, but in Sampras case, it was about his powerful legs. Likewise, when Sampras's foot speed dropped, his groundstrokes suffered. About Fed not crouching as low as a Sampras, well again that's more a end-result of his swing.
The extreme counterexample would be a Nadal. Even when he's using a flatter stroke, he doesn't really move toward the ball with his feet. He must rely completely on his hip turn and then his arm-follow through to produce his most power.