I use external screens just fine. I can't even think of a situation that's a big issue:
- 4K laptop screen and 1080p external, just use integer scaling
- 1440p laptop screen and 1080p external, use 1.3x font scaling and everything looks fine
I currently have a 1440p laptop, a 4K external, and a 1280x800 projector in my work-from-home setup. The external screen replaced a 1200p one before. I use sway that supports fractional scaling per screen in whatever setup I want. And yet I prefer to just set 1.3x font scaling for everything and not touch the scaling at all. Everything looks great.
Fractional scaling is a missing feature for some people and Linux desktops are definitely behind. But compared to font scaling I don't see how it's really much more than a little bump in functionality (some controls sized a little better) for a big drop in performance (calculating >2x the pixels in a lot of situations) and even some loss of sharpness.
It's probably a huge preference thing. I've seen people online waiting impatiently for fractional scaling because things were too small in their 1080p laptop screen otherwise. Even though 1080p on a laptop is sort of the definition of 1x.