Also: when was the last time you shot film side-by-side with digital?
IMAX is close to 6x7 film, which is perceptually about the same as the 5D Mark III--at best. Scans are done at that resolution to avoid aliasing. And film has more detail before extinction than digital in this case (due to the larger sensor), but the mtf falls off to <50% or so pretty fast whereas digital stays sharp to extinction. I've seen 6x7 prints (Velvia) side by side with 5D Mark II prints....it's close. Really close. The area under the mtf curves, assuming excellent lenses, is similar with high end full frame and IMAX--and that's the closest measure we have for perceptual sharpness.
Color negative film has more highlight detail but less shadow detail. At best we're talking 14 stops total....cameras are now 14 bit and getting close, they just clip highlights faster for much cleaner shadows (and thus much higher perceived resolution--6x7 is way grainier than FF digital!).
And who shoots IMAX? Like no one. Most people who are shooting on motion picture film (which is still way out of the price range of the average amateur) shoot 35mm, and the Alexa beats 35mm in every possible category except maybe it has about .5 stops less highlight detail.
Film is pretty terrible, technically. That you need to invoke IMAX, a little-used format, testifies to this. (Though 6x7, a very common format, has virtually the same frame size, which confuses me. And 4x5 actually does beat most digital, excepting the 80MP backs maybe. 8x10 trumps everything!).
That said, it still looks really, really great. But of all the arguments to support it, this is one of the most ridiculous I've read, sorry.