XP was the peak of desktop customizations. There were "theme packs", one of the most popular being a Vista Theme Pack. The teen in me, with a Nokia 6600 besides the computer, was in awe when a single installation of Vista Theme Pack and rebooting a couple times meant that everything on my 40GB HDD Pentium computer was changed from the login screen to icons, wallpaper, fonts, shell, file copy boxes, disk space meter,…
Are you aware of the very large number of desktop environments and window managers available on *nix systems? “Skins” were popular in the windows ecosystem around XP, but it was far from the peak of customization.
It was most definitely peak customization.