Ok, just a couple of comments. First off, I've made a pretty good living throughout my career spec'ing, installing, programming VFD/motor combos in countless applications. So yes, while I move my lips when I speak. People have seen fit to listen intently and open their wallets while doing so.
I don't have any hands on R&D with the diamond polisher, so whether or not the end result (polished balls

) can be better had with oscillating spd/direction during the cycle, I cannot say. In my humble, uneducated pool ball polishing opinion, I'd say probably not. Take that what you think it's worth, but don't let the fact that I'm agreeing with you sway your thoughts on my opinion.
I have no dog in the "better polisher" fight. Simply stating that a VFD/motor combo can be driven at the spds you think they can't and be just as reliable as a full nameplate motor geared down.
I said earlier that one of the greatest things about the diamond polisher, is it's simplistic design. Going to a VFD/motor to perform the same task is a needless complication. <--again, my uneducated ball polishing opinion