I have a multi-monitor setup with one monitor rotated. xfce4-display-settings does a great job of allowing me to rotate and move the monitors about to match their physical layout, but the only way I could get it to not be all wonky at the lightdm-greeter login screen was to dive into xrandr commands. It really shouldn’t be that hard for a user to specify how the monitors are configured for their system as a whole.
Sure thing, but how about on a multiuser system, where each user has different workflow, hence the settings will be quite different for the monitors layout for those users? Who is overwriting who’s system wide settings in that regard? Of course the lightdm-greeter will seem wonky, and in case you want it to follow your particular setup, for your single user system, needs to be modified manually …
The person who has sudo access, and is administering the computer, obviously. The standard use case is generally a single user, and how many cases are there going to be where different users re-arrange a multi-monitor setup? They can, of course, have their own user settings, as is currently the case. The problem is that there’s no way to set a sensible system default without diving into xrandr or xorg configuration, which are a long way from being accessible.
All that should be addressed to XFCE developers (in your case). Also, for those that use Wayland on different DE, example Gnome, there is no xorg config and the xrandr will not work.