Funnily enough, the real transformative advice was simply to count! I'd never really counted while playing before, assuming pridefully I could just feel the pulse, but with the Bach piece I'm working on there are precise releases and a lot of entries on the second sixteenth of a beat. Yesterday was my first ever practice session where I counted throughout, and while doing so meant I couldn't play blazingly fast and had to take a step off the accelerator, so to speak, and there were a fair amount of hiccups and head-scratching moments, it really worked. My Chopin Mazurka, which has been a bit of a hit to the self esteem, because I have the technical bits down and the entire thing memorized, yet it never sounds decent when I play it, suddenly had flow and rhythmic drive, and there were even parts where I had been "ballparking" the rhythm and annoyed with myself how clunky it was in my hand (thinking the issue was a general lack of dexterity) that resolved completely whilst counting.
To really test out the efficacy of counting, I gave the Bach WTC 1 C minor prelude a test run. I had been thinking my issues with the piece were purely technical, having heard virtuosi zoom through it with ease with me struggling to stay afloat around quarter notes 120 to a minute. When I play it it tends to start start off ok, but the hands struggle to stay in sync and the overall feeling is chaotic, a far cry from the spirit of the work. With counting, immediately the hands stayed together so much better and it sounded as if it had pulse and flow, which even in the past when my hands could manage to play at the same time, there didn't seem to be pulse and musicality.
So I think I'm already sold on baking in counting into my regimen, even my warmup, to really hammer home the idea. It's a bit of a situation where I have to take a step back to move forward (with the three voiced Bach work there's too much going on to immediately be at tempo, counting and keeping tabs on all of the voices), but in the Chopin, since on the whole the piece is rhythmically simple I have no trouble playing at the quite fast veloce tempo, and on top of that my playing feels more structured. It's funny how something I've always been skeptical about suddenly fixed these nagging errors I was beating my head against the wall to fix.