I suppose the default status is important to catch newbies. But besides that I don't think it matter so much outsides of ubuntu and mint(I get the impression that their user bases culture is different from the rest of the linux distros in that they are "loyal" to the default software in higher degree)
In Arch Linux its look like gnome shell is installed in around 24.5 % of the computer that has the "pkgstats" package installed. kdebase-plasma is installed in 26.5 % of the computers. xfdesktop has 24.5 %. Openbox 24.5 %, i3-wm 6.5%
Besides the low number for i3 I think the number is as expected. Kde is biggest but it almost even with gnome and xfc.
https://www.archlinux.de/?page=PackageStatistics