This is actually demonstrably wrong. Here are 3 screenshots I took in Half Life 2 at different resolutions, all downsampled to 1080p for your convenience, so you can't argue with "sitting way too close to your screen". All 3 screenshots were taken at maximum graphical settings, including AA. Without AA, the differences would be even more obvious. I recommend opening all 3 screenshots in a new tab and using CTRL+TAB to see the differences even more clearly.
1080p
1440p
Notice the increased detail in the fence and the antenna on the house.
2160p (4K)
Notice the increased detail on the crane (especially one of the 2 support cables is now much more clearly visible), the antenna has gained even more details, but the most obvious improvement is in the tree in the background on the left, where some of the branches are now being rendered, when it used to be invisible before. Fun fact: without AA, the mesh in the fence would be barely recognizable in 1080p and 1440p, and perfectly rendered in 4K. The tree in the foreground (at the top right) would also have holes in 1080p.
There's a reason why super resolution is a thing.
By the way, I originally wanted to take a screenshot at 3240p (5K Dynamic Super Resolution), but only the top left corner was visible (even in the screenshot), which wasn't very useful for comparing.
I mean, you guys are free to prioritise framerate over resolution, that's your choice. But to claim that there is no increase in (visible) detail is plain wrong. Have fun playing with your microscope, but stop assuming that everybody's as blind as you are.