Better Rotation and Compression

Compressing the ball means striking it while the clubhead is still descending, with the hands ahead of the clubhead, so the low point of the swing arc sits after the ball. It is a low-point and shaft-lean question rather than a strength question. Fix it by moving your weight and your lead shoulder toward the target in the downswing so the arc bottoms out in front of the ball, and use a line on the turf to check the divot starts after the ball rather than before it.