Yeah, I have a hard time believing that someone with normal eyesight wouldn't be able to tell 1080p and 4k blu-rays apart. I just tested this on my tv, I have to get ridiculously far before the difference isn't immediately obvious. This is without the HDR/DV layer FWIW.
10 feet is pretty far back for all but the biggest screens, and at closer distances, you certainly should be able to see a difference between 4K and 1080P.
For the 30 to 40 degree FoV as recommended by SMPTE, 10ft is further back than is recommended for all but like a 98in screen, so yes, it’s too far back.
It very much depends on the particular release. For many 4K releases you don't actually get that much more detail because of grain and imperfect focus in the original film.
