People have been saying "You can't tell the difference between X and Y" since the dawn of HD graphics in general.
"You can't tell the difference between HD and FHD." FHD and QDH. QHD and 4K. 4k and 8K. 60FPS and 120. 120 and 240. A higher resolution texture. Higher resolution audio. A higher resolution mesh. Etc.
Every single time someone makes the claim it makes no difference, yet we do it regardless.
For something that seemingly makes no difference, people sure seem to continue improving it regardless. And shockingly, consumers seem to really enjoy the products too.
Maybe. That test doesn't cover everything. Not all content, not all TV sizes, not all individuals, not all display technology, not all environments, not all compression tech, etc.
What about images that use HDR10+? Or Dolby Vision? What about completely un-compressed lossless video? What about common compressions like X264 and X265? What about on an 80-inch screen? What about in dark vs bright scenes? Or even environments? (Human eyes handle images differently at low vs high brightness)
I'm not saying the data is worthless because it's not, but I am saying that I think it's too sweeping to say it's completely un-noticable. Not enough data for that conclusion. Vision and display technology are both very complicated topics and there's always room for improvement IMO.
Pixel density has diminishing returns, we've known forever its not linear. Its the same reason why phones aren't all 4k by now, nobody can tell the difference.
Every single upgrade in resolution has been diminishing returns, and that hasn't stopped anyone from doing it anyways.
The only reason it will ever stop is if we hit major technological or even physical barriers. And even then, we'll most likely just move onto another technology that allows yet higher resolution.
