Whilst some components inherently use more memory than other viable alternatives (gnome-shell's JS runtime), gnome-shell generally has a lot more components and thus features than the more barebones window managers - and this should always be pointed out. Of course, if you are certain you will never need the extra functionality, then don't use Gnome. But generally, I don't think it makes sense to compare plain window managers with desktop environments. I think an interesting comparison would also be looking at quartz, the macOS window manager/desktop environment.