This is simply false and it's blatantly obvious that anyone who says this doesn't own a 4K set. The same crap was said about 1080p when they were going for substantial premiums over 720p and 1366x768 plasmas.
A 55" 4K set at a viewing distance of 8-10' is enough to see substantial benefits. Don't forget that it's not just about 4K resolution, but 10-bit color and HDR. The difference DV/HDR makes is HUGE. So big that you will try to avoid watching SDR content whenever possible.
I know that the first thing I look for is whether a movie or show has DV/HDR before making my choice. 4K and 1080p SDR content still look glorious on my LG C8 but once you get used to Dolby Vision and HDR10 w/dynamic tone mapping it's impossible to go back to a first gen 4K only TV (i.e. Sony 900B) or any 1080p TV.
What does this have to do with HDR and 10-bit color? You're comparing old 1080p TVs to 4K, not 4K to 8K. Straw man argument.
Let's get back to reality and talk some real numbers based on real math and science. A human with 20/20 vision has a certain visual acuity of one arc minute. Beyond a certain resolution, they can no longer perceive a difference between pixels as they begin to blur together. There is a limit to human vision. A 55" 4K display has an ideal viewing distance of a little over 6ft. Any further and a perfect human specimen will not be able to tell a difference. If you have any sort of corrected vision (glasses, contacts) your numbers are likely to be worse, even corrected. Even so, assuming you have perfect vision, a little over 6ft between your couch and TV makes for a pretty small living room setup. Not ideal, but that's okay if that's what you're dealing with and you don't mind that. It's at least doable.
However, let's take things a step further with 8K. Remember—8K both doubles 4K resolution in both width and height. Factoring this in, a 98" 8K display is even worse than your 55" 4K TV. Much worse. The ideal viewing distance of a 98" 8K display is a little over 3ft. Any further away and it all blends together. Now you can argue all day if you want, and you can be sure that I won't respond—the fact of the matter is that you're wrong because these numbers are based on math and science. No amount of wishing is going to change that. Human vision at 20/20 cannot resolve anything more than one arc minute. These calculations are based on that reality, which are based on scientific observation and testing. Science and math always come out on top. To achieve the same visual acuity as your 55" 4K TV, you would need approximately a 190" 8K TV if you were sitting a little over 6ft away. For now 8K TVs are utterly pointless, worthless, marketing jargon for people who don't know the difference between a pixel and a pica. There is no reason to have one in your living room and are only even coming close to being useful for large desktop displays that you sit close to. But even in that situation I'm not convinced that it's worth it because you'd need a 48" 8K display at a distance of approximately 18" at your desk and the viewing angle for that sounds neck-breaking painful.
As for content, where is it? Japan? I know NHK that has an 8K stream and will broadcast the 2020 Olympics in 8K. Good for them, there is that one thing plus some videos on Vimeo. But show me a link to buy or stream an actual real 8K movie. And no, some random Vimeo link by some independent studio short film project doesn't count. I'll be waiting.
TL;DR: 8K displays are pointless until wall-sized displays are widely available without needing to take out a second mortgage. The human eye at 20/20 can't resolve beyond one arc minute and therefore can't tell the difference between a 98" 8K and 4K TV unless you're about 3ft away. There is no content and the price is ridiculous. 8K TVs are an excellent way for fools to part with their money.
