I agree 4k at higher fps is way better most often he time. Just one use case people may not be aware of for 8k is video editing. You need really high resolution for editing videos else you're at risk that you introduce artifacts and blurriness when editing. Especially if you decide to zoom or crop.
This applies even if your final video is 4k.
Again, I'm on the 4k120 boat. Just wanted to share one common reason 8k is desired by some people.
There is no point to a small handheld device being in 4k.
2k /maybe/.
You would have to have literally super human vision to tell the difference between a 2k and 4k display the size of a phone unless you held it something like 2 or 3 inches from your face.
At which distance most people cannot focus their eyes anyway.
It's for video recording, not the screen resolution. I'd say for archival reasons it's perfectly okay to record in 4k even if your phone display is not in 4k. Sometimes I like to view my recorded videos on my 4k TV to be watched with friends and family.