Hmm. You might want to get an eye test. Not being snarky: when I was 45 or so, having had "perfect" eyesight, someone suggested I get mine tested. Turns out most people loose the ability to focus at short distances with age, but the brain doesn't clue you in. Not being able to tell the difference between 1440 and 4k would be consistent with this. For me even at 13" screen size 4k is very obviously better for coding.
With a 55" screen you'd have to be within 3.5 feet to be able to see a difference with 4k. So no eye test needed. Your brain is either lying to you or the 4k screen you tested with is better than the non-4k you used.
There are many things incorrect about that blog's approach. As others have pointed out, this isn't like HD Audio, where people literally cannot tell the difference between normal CD quality and HD Audio in any realistic test. I can absolutely see the difference in a 4K screen, and I can tell if even a smallish laptop screen is 4K or not from much higher distances than normal usage. I remember the first time I saw an Apple Retina display on a tiny laptop from across the room and said "holy shit!" out loud and walked over because I could see how sharp it was from meters away.
First of all, 20/20 vision is the average, not the best. Many people have substantially better than 20/20 vision. I remember laughing that I could read the super fine print "copyright notice" at the bottom of the eye test that is about 1/3rd the size of the smallest font in the test itself.
Secondly, the eye is complex, and has surprising capabilities that defy simple tests, which are designed as a medical diagnostic tool, not as a test of ultimate resolving capability. For example Vernier Acuity (1) means that much higher resolution printing (and screens) are required than one might think based on naive models.
Actually, I don't have sources on hand, but I believe average human sight is better than 20/20. It's just that 20/20 was decided on as a standard for "good enough". I believe stemming from a military standard set long ago.
I don't know what the methodology of that site is, but it's certainly flawed when it comes to computer monitors. Based on their calculator, I shouldn't notice the difference between 1080p and 2160p when sitting 2 feet from my 16" laptop monitor, but the difference is night and day. I don't want to get into a philosophical debate, but if I can see the difference that your equation says I shouldn't be able to see, the equation is wrong, not reality.
This reminds me of the pervasive "your eyes can only see 24fps" myth, I guess people crave evidence that what they have is "good enough" and others are just being elitist?
Well, you will definitely see more than 24 fps, but that might or might not translate to better experience. If you want the cinematic effect for a movie, it will be 24 fps, otherwise you will get the soap opera effect.
For other uses, like fluid animations or games, you want as high as possible.
I wonder if the "Cinematic" look at ~24fps seeeming less tacky than the "Soap Opera" look at ~60fps has just been trained into us via familiarity though.
If we lived in an alternate universe where cinema was all 60fps and soap operas were 24 would we think that 24fps looked tacky instead?
On the other hand I think there's definitely some objective effects in play here too - CGI is a lot easier to make convincing at a lower framerate and added motion blur.
You're conflating two separate things - HDR is the specification for > 8 bit dynamic range, 4k just specifies 3840 x 2160 resolution. You can have displays that are HDR but not 4k, and vice versa.
I absolutely benefit from a 4k screen even in a small form factor. 768p is "enough" in the sense that we all got stuff done on such screens for many years, but the increase in text rendering quality with higher PPI screens is tremendously worth it to me for the reduced eyestrain. 4k is still noticeably better than 1440p. I wouldn't be surprised if 8k is noticeably better still (although with swiftly diminishing returns of course).
The reverse is also kinda true... Many people when they say "I like high resolution" mean "I like to fit lots of stuff on the screen at once".
If you're in the latter crowd, you can configure X or Wayland to render to a 4k screen buffer, and then downscale to fit the actual screen. Yes, downscaling no longer means 1 pixel=1 pixel, which introduces some blur, but unless you're a 20/20 vision kind of person, I doubt you'd be able to tell without your nose touching the screen...