There are good 4K gaming monitors, but they start at over $1200 and if you don't also have a 4090 tier rig, you won’t be able to get full FPS out of AAA games at 4k.
I've seen analysis showing that DLSS might actually yield a higher quality image than barebones for the same graphics settings owing to the additional data provided by motion vectors. This plus the 2x speedup makes it a no brainer in my book.
Also, ultrawide monitors. They exist, provide more immersion. And typical resolution is 3440x1440 which is high and and the same time have low ppi (basically regular 27" 1440p monitor with extra width). Doubling that is way outside modern GPU capabilities
