Following the back and forth. I have to say, posting this side by side is a real head scratcher.
The reverse "C" created by these two swings is a huge fundamental flaw.
And the capitol "C" created by the hitter on the right is not high level.
So the backward "C" equals too much weight on the backside OR a lack of weight transfer or centering(balancing) the weight between the legs? That sounds like a spinning backside....