You can say they're off balance all you want, but if you want the center of your mass to go through someone, you're going to have to give it to them. .
If you want the center of your mass to go through you lean back like a bow. It's often likened to a Y shape.
The Karateka is making an R-shape. He is losing the weight transfer regardless of his hyper extention.
You'll just have to take my word for it. Or just watch the best guys do iit like below