Another linux+i3 user here, I've not tried 4k yet but you confirmed my suspicions.

I did a lot of research before buying an xps-13 and went with the 1080p version due to basically all the reasons you just stated + poor battery life and video performance.

I have hope for the future though... what would really make transitioning easier is a way to automatically upscale incompatible programs, even if it means nearest neighbor scaling at least it will make them usable on super hi-dpi monitors.