Given your observation, I'm guessing you have not used i3wm very much. i3 is extremely flexible and powerful. But as with most Window Managers, i3wm is geared towards those who prefer to build a highly customized environment. If you haven't already, this is a good read. https://i3wm.org/
Right on point ; I use it years ago as my daily driver in terms of wm, but never went very far in term of customisation. Now is maybe the time to look at it again, thanks for the link!
It's interesting how close they are to one another. I don't understand why there is a Dropbox column and didn't see it mentioned anywhere else. Another question I have is how much RAM the system has in total, as that seems to affect consumption.
Thank you for noticing my omission. I added the following:
NB.: Dropbox is shown because it runs at login and is a large contaminant in terms of memory utilization on each window manager (setup). If you do NOT use Dropbox you should expect your idle memory use to be lower than my total by some 600MB.
That makes way more sense. I remember plasma idling around 1.4 GiB back when I was running Arch with 16 GB of RAM. Although right now on my Kubuntu machine at work, I'm using 3.0 / 110 GiB just being on the desktop.
FWIW neither KDE nor gnome are Window Managers (WM), they are Desktop Environments (DE). WMs are significantly different from DEs in terms of what they provide and how they are constructed. WMs are more of a builder's kit and less of something you just install and use. If you like doing things in a specific, unique manner you might enjoy WMs. Be advised they are, almost always, much more detailed in terms of their installation.