Alan,
The human eye is often said to resolve one half minute of arc...at 14' distance that means the eye can detect something as small as. 0.049" or 1.24mm.
A 75" monitor measures about 65" horizontal, so that means a single horizontal pixel is 0.43mm, so less than the eye resolves at that distance...just don't sit closer than 58" and you won't be able to detect individual pixels (which can be seen in the front rows of the movie theater!)
What you point out is valid outlook, but that in turn raises the question of why the obsession for more than 16MPixel, you could crop the photo to remove 75% of its pixels with zero apparent perceptible loss of detail compared to what our 4K monitor can present. Or put anoither way, when we send a 16MPixel file to display on our TV, we are sending 4X as much data as it can resolve, lengthening transmission time.
Those calculations pretty much match my real-world experience. Thanks for spending the time to provide them. I can see the difference between a picture of 1920x1080 (2K) vs 3840x2160 (4K) displayed on the 75" TV screen when I sit about 5-6 feet from it or closer. So people sitting in the family room nearer the TV can notice the difference. OF course, I usually sit 14 feet back on my recliner, so the difference is not noticeable to me. One thing I have noticed. That pictures and movies taken with higher resolution still look sharper overall. Don't know why? So I'll shoot movies at 4K. It also provides more cropping room than movies shot at 2K. I use Adobe Premiere Elements to create the video slide show which allows me to zoom in on the video or even stills for that matter. when editing and creating the video. With stills, I'll use Lightroom to edit first. I'll create jpegs for the video with a vertical height of 2160 (4K). There's no point using more resolution unless you have an 8K TV. I dump the shows on to memory cards that are then plugged into the USB jack of the smart TV ready to show. I used to use DVD's. But most people stopped using disks. Also, they're too slow and memory limited for 4K movies. I do have Blu-ray player. But most people don't have those either.
Of course, with stills, I also have cropping room if I'm shooting at 20mb since I only need 8mb to convert over to a 4K slide show. Another factor is I make videos of my slide shows which provide a 4K 3840x2160 output. I could display the full picture that would be downrezed to 4K by the TV. But video slide shows allow me to add music, title, credits, annotations, fades, transitions, etc. It also allows me to download to YouTube to show others.
YouTube allows 4K as in this example I did. In settings, you can select 4K, 2K or even smaller resolution from YouTube if you want to do you own comparison on your TV or computer. It's stills only in video format.
If you want to see a movie that has 1080 movie clips and stills mixed in, check this one. 1080 is the max setting though.