Keep in mind also, that 20/20 vision doesn't represent the pinnacle of human ocular acuity either... It's a "Snellen fraction".
That chart is pretty much in the same ball park.
It recommends the following viewing angles for
720p -> between 11.5 degrees and 21.2 degrees, or 111 pixels per degree to 60 pixels per degree
1080p -> between 21.2 degrees and 31.2 degrees, or 91 pixels per degree to 62 pixels per degree
2160p -> between 31.2 degrees and 61.1 degrees, or 123 pixels per degree to 63 pixels per degree
So true, 20/20 vision is on the edge where higher resolution is considered worth it, same as the chart I put up there. In fact, if you're already at or over 60 pixels per degree that chart considers higher resolution not worth it.
But also very true that it all depends on the quality of upscaling. Modern techniques upscaling to 4K are much better than last gens sub 1080p to 1080p software scaling, or 720p to 1080p by the average tv. Next gen shouldn't have any of those issues and 1440p is plenty with good upscaling, 1080p will even be more than enough for most (most people's viewing distance is in the 20 degree range) hence Lockhart.
Sitting so close the viewing angle exceeds 40 degrees is also no good for a lot of games. I already had that issue at a 31 degree viewing angle (12ft from 92" projector). You lose oversight and some games (especially one where you had to control two things with both sticks at the same time on either side of the screen) become much harder than they should be. In fact Super stardust on PSVR is unplayable since you have no overview to where the enemies are coming from, you have to look back and forth the whole time. I also kept crashing in Burnout paradise on my projector since looking away at the map takes longer the bigger the screen. (Eye saccade speed limitation) Smaller screen, can more easily keep track of more.