What is important? The pixels showing the ennemy, the mosaic on the wall I like to discover, the shadow that change with the folliage of trees and perhaps the ennemy comming in my back? Even if I take the example of the shadow that in the beginning was not important and for that badly renderend to save some time budget and because an ennemy is comming in my back the sahdow became very important for the clue that there is something/someone in my back, the change in the quality of the shadow would kill any surprise effect :(
Now for the advantages of upscaler, Shadow of the tomb raider (with very good hardware) run at 137fps in 1080p and about 60fps at 4k. In these conditions, upscaling keep a very good framerate and let me play in 4k. Not bad at all :)