This site asks for 1.5 Go of ram https://ubuntugnome.org/, Ubuntu 20.04 asks for 4 Go of ram. Compared to the 30 Mo for IceWM in the article (apple to oranges, I know, but still 3 orders of magnitude), or the 300 Mo for KDE. The author also notes that since XFCE switched to GTK3 they use more resources. That seems to be plenty of basis in reality. Perhaps you mean something else by "resource intensive"?