I don’t think you covered the difference between 70mm and IMAX 70mm. One frame of IMAX is basically 3 frames of normal 70mm. So it is physically 3 times bigger

I’d say that yes it’s a marketing technique, but for these releases it’s not a gimmick. If you have a chance to watch a film in 1.43:1, you should try it. The difference is how big it is, and especially how tall it is. Most theatres don’t physically have the size for it. Film could be gimmicky, but I can clearly notice the difference. (Was at a film release that had to fall back to digital at a couple points, and it was very obvious to me, but not my friends with me.)

What’s gimmicky is when normal movies release for IMAX without filling that full aspect ratio. Or when you have a tiny IMAX screen