After last post, I'd concluded that I just wasn't swinging the right way because the impact pattern was mostly from "in line with, or to the RIGHT of" the nub in my short bat as a RH hitter. And I concluded that ... it was roughly consistent with my slicing with a mini half bat as opposed to hitting it flush.
So at that point I got some duct tape and threw it on the barrel of the bat and did some tee work and got back to trying to isolate hand pivot, and after a few sessions where I felt like I made some progress, I decided to return to the cage and take some hacks off the machine. This time for more direct and immediate feedback... I first sprayed the bat with some Dr Scholl's foot powder - the zinc oxide in there is basically white spray paint that rubs off pretty easily. And it was VERY clear where the impact zone is... and today "everything" was "in line with, or to the LEFT of the nub."
So that's progress, at least? I felt like I needed to move the impact zone roughly 90 degrees from where it was. And though I certainly haven't accomplished THAT yet, it's clear that the impact pattern has moved LEFT of where it was, so I am more confident that I am NOT using my arms to push as much. My swing cue for this session was... start resting on the shoulder and try to just snap out from there in a check-swing snap-stop sort of motion... as a means of guarding against "using my old swing".
Anyway, progress of a sort. Shortens the feedback time for me as I am trying to verify whether "that felt right because I just used my old swing" or "that felt like I used the new swing, like I meant to" based on whether I hit the correct part of the bat!