Maybe it is merely a documentation issue? I keep hearing stories on the one hand of people (such as yourself) who say they failed to get X working with multiple displays... and yet, a ton of software seems to exist predicated on the notion of working with multiple displays (even i3) and a number of actual users claim to have multiple displays working.
https://ptgamr.notion.site/xrand-4k-mixed-monitors-7a026e534...
^ maybe this would be useful? This seems like a pretty simple single run of xrandr that configures multiple (three, even) monitors on X all at different resolutions and ending up at different display scaling (including one fractional scaling). Like, looking at this, I feel as if I should be able to get this working myself, were I to have multiple monitors (I don't on my Linux laptop).
FWIW, I love the idea of helping someone not be sad about having to switch to Wayland by getting them back on X with all of their happy software working, and so if you want to try to debug whatever your issue was together, I'm game. To me, what makes Linux fun is all of
the random combinations and hacking we can do together, and it just seems like people are both losing that ethos and even saying we are wrong for enjoying it, and that makes me a bit demoralized :(.