With the rapid development at XFCE it will take a while until I have to think about it, although I'm currently using Fluxbox almost exclusively anyway
Personally I am not too interested in the RAM demand in idle mode. So 50mb more or less.
Current Mint /Cinnamon e.g. had 750mb, but I didn't investigate further, on the disk is now the KDE beta.
Just compared, my xfc has less than 600mb after startup, the KDE beta (where there have been some updates) is also less than 600mb.
If you want less, you have to use Fluxbox, because after what I "hide" there I get below 350mb.
I find the behaviour under heavy load more interesting
I recently wrote something about it on Facebook, but my focus was not on ram requirements, but was related to thread load and thermal behavior of the very first version.
The subject was settled, but while I was at it, I still did my stress test:
Current handbrake from the test repo, freshly installed, identical settings, format conversion of a camera video with 1920x1080/120frames/sec to 1920x1080/30 frames, (vfr, rf21, preset:placebo)
Original file 800mb (sony a7III video, losless)
target file resulted in a size of 43,4mb each time
averaged from 3 runs each
fluxbox 53,16 frames/sec
xfce 52.82 frames/sec
kde 50,14 frames/sec
And all 3 versions oscillated from 1:30 min between 93-95 degrees celsius and cooled down to 45 degrees within one minute after completion.
I repeated the experiment today under more realistic conditions.
More realistic means, in addition Firefox with 2 open tabs, file manager open and QMPLay2 working on its playlist (I almost always listen to music on the PC).
The two pictures actually say enough
KDE Beta

fullscreen
https://web57.ws/test/kde2.png
MX-Fluxbox

fullscreen
https://web57.ws/test/flux2.png
The minimum speed advantage of Fluxbox this time was 1.5 frames/sec (2,5%)
Translated with
www.DeepL.com/Translator (free version)