5-6 years.

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.

weird, I wonder what distro you were using. Even 5-6 years ago, multi monitors just worked for me - hell, I had a retina screen at that time and it pretty much just worked too.