When I recently switched to self-hosting, I was almost certain since I was so used to 4k that I’d need to self-host all 4k content.
I realized the whole time most of the streaming services I used barely even gave me 4k content, and when they did it was so low bitrate it was basically comparable to 1080p.
So now I specifically download 4k movies for ones that I really care about being 4k (e.g nature documentaries) and for the rest 1080p is more convenient space/time wise.
The differency between FullHD and 4K is very noticeable with THX-recommended viewing angles. I watch 98” from 3 meters.
OP is right, at the typical TV pixel per angle (TV distance + screen size), 2160p is a waste. That's also why I always tell people to switch on performance mode on all console games that support it. Doubling your FPS for an imperceptible resolution decrease is a golden trade-off.
Ironically, monitor pixel per angle is still often too small. For typical desk viewing distances, you want 2160p at 21" and 2880p at 27". Most people that have big monitors have 2160p at 27".
Note that ultra-wide or not doesn't matter if you express the resolution you want in the vertical
This is then usually combined with the 60 PPD visual acuity quasi-myth, and so you get 1800px, 1920px, and 2400px horizontal resolutions as the bar, mapping to FHD and ~WQHD resolutions diagonal size independently. From these, one could conclude even UHD is already overkill. Note for example how a FHD monitor of exactly standard density (96 PPI, so ~23") at 32° hfov results in precisely 60 PPD. That is exactly the math working out in its intended way afaik.
At the same time, Mac users will routinely bring up the Pro Display XDR and how they think it is the bare minimum and everything else is rubbish (*), with it coming in at a staggering ~200 PPD, 188 PPD, and ~150 PPD at 30°, 32°, and 40° hfov respectively. Whether the integer result at 32° is just the work of the winds, who knows. It is nonetheless a solid 3x the density that was touted so fine, you would "not be able to see the individual pixels". But if that was a lie back then...
The pixel density (PPI, PPD), viewing distance, and screen real estate discussion is not one with a satisfying end to it I'm afraid. Just a whole lot of numerology, some of which I sadly cannot help but contribute to myself.
(*) not a reliable narration of these sentiments necessarily
Uh.. what?
You usually sit 60cm from your monitor, but 3-6m from your TV. It completely changes the math, which lets you "cheat" with ordinary TV sizes (50"-65") because you will not or barely notice the difference between 1080p and 2160p.
The other way around, your monitor won't really get the 'retina' effect of not discerning pixels until you hit ~220 PPI.
Never will be convinced picture quality improves anything.