I clearly remember that when Windows introduced auto-snapping/auto-scaling windows, I looked and giggled as yet another KDE feature made its way to one of the "bigger" environments.
It's really well working in these days, but it was not like that until recently. I remember setting up Xorg.conf to get my single monitor working as it should.
Yes, Auto configuring X.org is older than that, but drivers, Multi monitor setup and other related things came later than that.
Even if X had proper support for multiple monitors, drivers were very finicky at the beginning.
While most of the work has vanished for single monitor setups around that time frame, multi-monitor setting wasn't very reliable and deterministic under xrandr came around and drivers added native support for that.
*: randr came around 2003: https://cgit.freedesktop.org/xorg/xserver/log/randr/randr.c?...
And I definitely touched xorg.conf a bunch of times even a few years later.