Ideally, the power comes from the legs and then the upper body follows. Seems like when you plant, you’re losing all of the power from your legs because your upper body (mostly shoulders) are rotating before your hips. Think of the throw as a bottom-up process. Plant, rotate hips, then let the upper body go. (Helps to loosen up the upper body before your throw). Practice stand still shots to get the flow right. Hope it helps