Or people who argued that "4k is pointless, you can't see the different with 2k anw".

For gaming or videos I actually can’t tell the difference between 4K and 1440p. For text rendering I absolutely can.

As an aside, many 4k/1440p videos are not really 4k or 1440p in the same way a monitor is 4k/1440p. Mostly 4k/1440p light levels, but less than that w.r.t. color information.

A common video subsampling setup is 4:2:0.

https://en.wikipedia.org/wiki/Chroma_subsampling

In addition, common video compression techniques (at least the simple ones that I could still understand) basically reconstruct blocks of pixels. Reconstruction is lossy, at best.

If I had to guess, something similar could be done in games as part of their optimizations.

Something similar is done in video games through two technologies (in addition to colourspace trickery): DLSS and “dynamic resolution”

This really depends on the size of the screen. For most laptops, I'd argue that 4k is useless; 1440p is high-res enough that you get perfect clarity anyway.

For 83" TVs you obviously need more pixels to get a good viewing experience because you don't position yourself several meters in front of the screen to make the pixels unnoticable.

I think even for phones anything above 1080p, is kinda pointless. Just a drain on the battery.

For me, there's only a difference for the text console. For GUIs I have to halve the resolution to make things usable so it doesn't really help anything.