@timbray One thing to keep in mind is that those "resolution" settings are lies. Your monitor's pixels are physical objects, so you're just telling the Mac what kind of downsampling to do. Apple is conflating "I want my text and icons to be bigger" with "when a program tries to draw a pixel, smear that out to 3.7 pixels instead".
It is *possible* that if you have your "display resolution" set to 1080p, a video player will still have access to native hardware pixels, but I haven't checked.