I think it's misguided to say things like "IMAX 70 mm has an equivalent of 18k resolution." But have you seen a 70 mm IMAX projection? In my experience, the 70 mm image looks noticeably sharper than an equivalent 4K digital IMAX projection.

1.43 IMAX 4K is also a great experience, but its resolution is a meaningful and noticeable limitation given its massive angular image size. It's a compromise compared to a more traditional 4K cinema screen (like a typical Dolby Cinema screen): with IMAX 4k you gain angular image size and lose "pixels per degree of visual angle." And both are noticeable!

I agree with you that the latter has all the advantages you listed, but there is still something truly special about the apparent resolution of IMAX 70 mm projection.