Pointer speed is too slow for hidpi displays; xorg is inconsistent with Wayland
Submitted by Tony Houghton
Assigned to Peter Hutterer
This bug used to affect both xorg and Wayland; it's been fixed in Wayland https://bugs.freedesktop.org/show_bug.cgi?id=99383 but not xorg. Well, not officially, but I found your patch for Fedora https://bugzilla.redhat.com/show_bug.cgi?id=1413306#c54 and applied it to Arch, and it works well.
I added a second stanza to the example xorg config though, using MatchIsPointer (which doesn't seem to match my touchpad for some reason) instead of MatchIsTouchpad because I also wanted my mouse speed to be consistent in X and Wayland.
I see you're concerned that it might make some pixels unaddressable. Did you find out how the Wayland developers addressed that concern? My opinion is that it doesn't really matter, because the point of hidpi is to provide more pixels than a user can see individually, providing smoother text etc rather than more desktop space.