I don't agree with how you are explaning a hitters video. The hands seperate and do not fire properly, until the shoulders initiate that came from torso rotation, that came from hip rotation that were all initiated from the heal slam. "yes there is more in there, but now we are just boring everybody" Just my opinion.You said the sawing starts from the ground up. That’s function. I just showed you that his hands are initiating the swing against the ground. That’s hands down not ground up. Anything in regards to ‘ground up’ is false. Even generally speaking.
PS.
Ground up is not literal. Proper sequencing legit works in steps.