> FWIW, I do see screen tearing on my X11 multi-monitor setup. I just don't care.

If you ever get really bored one day, and you have nothing else to do, and you're using AMD/ATi hardware, try enabling the TearFree option for your video card driver. Something like

  Section "Device"
   Identifier "AMD"
   Driver "amdgpu"
   Option "TearFree" "on"
  EndSection

in a new .conf file in '/etc/X11/xorg.conf.d' and a restart of your display server(s) should do the trick. It works fine for me, and has worked fine for like a decade or more.