You are pretty confused here. Dynamic swings are the result of dynamic body motions. Period. No doubt, dynamic body motions work better when one stands on firm ground: the reactionary ground forces from firm ground provides better support than muddy ground. However, why anybody thinks it is a good idea to describe athletic movements of the body as "using ground forces" is beyond me. Maybe it gives people the idea of crouching, then springing up, but it seems like a pretty vague and indirect way of doing it.
BTW, this thread was intended as an attack on instructors who, unlike Brian, talk about "using the ground" to create "shear forces" that will create rotation of the body around the front leg. Look again at the first post. Brian agrees this idea is goofy. That he interpreted this thread as a direct attack on him is unfortunate but not my fault.
I have posted many examples of what dynamic motions are used by the bombers. They all go from externally rotated and bent hips and knees to internally rotated hips and knees. If Brian wants to instead describe those movements as "using ground forces", he can. It's a free country. I'd tell people what the movements are and how to create them.
BTW, I don't think this is "one of the most un-dynamic swings on the net":