Okay, I think I see our confusion. Much depends on the specific theater in question, of course, but IME most theaters equipped with a standard (non-IMAX) 70mm projector are not the usual small multiplex screens. Many, if not most, are in older classic cinemas like the late, great Uptown in Washington, DC (1936-2020), which had a deeply curved screen 70 by 40 feet (21 by 12 m). It was the largest in the DC metro area, except for the Smithsonian’s IMAX theaters.
In more modern theaters, the 70mm house is likely to be the biggest in the plex, and have the biggest screen, since 70mm was the premium format. So in general, 70mm screens will be much larger than the average multiplex. And the difference in image quality compared to digital is definitely noticeable.
Of course, even the largest 70mm screens are rarely larger in total area than the average classic IMAX film screens (about 60x80 feet) because of the former’s shorter aspect ratio.
One of the problems with film is that, unlike digital, film prints can become scratched or otherwise damaged if not handled carefully. And given that only a tiny fraction of theaters still have film projection of any kind, the number of skilled projectionists is shrinking as they age and die. I daresay Nolan’s Odyssey has brought hundreds of old projectionists out of retirement.