Got the Leica S9D now. My impression is that it's basically like a luxury version of the AmScope. It does basically the same things in basically the same way but it does each of them about twice as well. Brightness, zoom range, clarity at high mag, depth of field, ergonomics are all substantially better. Build quality feels the same.
Overall I'm satisfied. I think that the research I did gave me realistic expectations, especially watching those random Youtube videos taken through the eyepiece. I am glad that I went for the more expensive microscope with longer zoom range because that's really the killer feature for me: going fluidly between "whole board" and "that 0402 over there." I'm also satisfied that I bought new because I really spent waaay too much time fighting with cheap optics in 2020
The S9 is compatible with my polarizing ring light from the AmScope (phew) but for now I prefer just using four gooseneck lights. Here's a video showing it off together with my preheater-on-a-lazy-susan bench setup. I'm not sure if the RPi camera is really doing it justice, I'm capturing at less than 1080p, but it's good enough for me for now.