Maybe if your couch is like 20 feet away. I can tell the difference from where I sit even with something like MGSV, a game that already looked clean at 1080p AND it was only upgraded to 1440p.
Edit: that said I'm not going to sit here and pretend 4k is like gods gift to gaming because it isnt that dramatic, but greater than 1080p res just looks nicer and is something I am looking forward to being standard.
I feel like on the X the improvement to 4k kinda depends on the game. Like in Fortnite, I remember the day it got Xbox enhanced with the high frame rate mode and it looked damn good, albeit a lil choppy on the inconsistent 45-50 fps. Then, they just blew that out the water when they did the 4k 60fps across the board. I wanna say the assets were improved too but I can't be 100% on that.
In the other direction, I played Gears 4, which looked fantastic to start, and then it got it's update. I wasn't nearly as impressed with the 4k mode, but the high frame rate mode was amazing. So I thought then that frame rate increase creates an illusion in my mind that the game is cleaner. But then I played Fortnite on PC. Night and Day difference. With all settings on Epic save for the Shadows and draw in, the game is definitely smoother at 144fps, but without HDR (my monitor doesn't support it) it just looks kinda drab, though it's smooth as butter.
So in conclusion, I think if you're going to rank what makes a game look better it would go in this order.
1. Frame Rate
2. higher resolution ASSETS
3. HDR
4. resolution (4k, 1440p...with a hard cut off at 1080p...anything below that is inexcusable)