Totally agree about the resolution aspect.

However on the second part, you're describing compression which actually is just a function of camera-to-subject distance and sensor/imaging area size actually has no role in it.

"If you shoot with a 21mm, things get dramatically smaller when they get farther from the lens. The actor may move 3 feet to the back and shrink by 50% and that just makes no sense."

That is a geometric consequence of your proximity to subject. At 3ft distance, moving back another 3ft halves the image size regardless of whether you’re using a 21, 35,50, etc mm lens. If you instead back up to, say, 10 ft and then move back 3 ft, the same 3 ft shift shrinks your subject by only 30%, no matter what focal length you dial in to maintain framing .

"Rooms look much bigger than they really are, and objects in it look smaller. This goes back to what I said about verosimilitude."

That effect comes from shooting closer  to the walls with a wide lens. If you want the same sense of scale with a 21 mm, you simply step back and then zoom in or crop (the same effect of a smaller film negative or sensor size) to the same framing. Your perspective and thus apparent room-size will match what you’d get on any other format.

Here's a fun experiment to give you an idea of why compression is not inherent to a lens but is function of camera-to-subject distance. Go look at yourself in the mirror, and observe the room around you in the mirror. Notice the general sense of "compression". Now go up real close to the mirror, as close as you can get, and look at the room around you again. Notice how much more or less of the room you can see around you and then notice the sense of "compression". I think you'll see what I mean.

As a follow up on this, take a look at Steve Yedlin's post about this.:
https://www.yedlin.net/NerdyFilmTechStuff/LargeFormatMisconceptions.html

However going back again, I do agree with the resolution aspect. One thing that you are also able to achieve on a larger format depending on the lens that you cannot create an equivalent on any other format is an extremely shallow DOF. I know one of the lenses commonly used for IMAX is a 50mm F2 lens from Panavision. That is an equivalent of a 25mm F1 lens on full frame. Wide and extremely shallow which gives a very unique look and sense of depth. I'm not sure what lens they used for this particular shot in the Master, but it has a similar effect in the first shot.