A DE is an integrated environment that includes... a WM with other "elements".
Anything else is only just... a WM with other "elements".
Again this is not opinion... merely definition.
see... Desktop environment
Again... I am more than familiar with Openbox which uses Mesa dependency.
However... PekWM is radically lighter because it uses only XCB
I'm also totaly familiar with... Tint2 (XCB)... Xfe (FoX) and SlimDM (XCB)
...just to name a few elements I have used for many years.
These desktop elements function more efficiently inside a DE.
EDE (it's in the USM) would be a high performance solution but...
unfortunately it's FLTK widget aesthetics are horribly outdated.
The FoX toolkit widgets are not fancy but
...they are far more modern than FLTK.
Which is why I chose FXDE.
It's toolkit (FoX) is magnitudes lighter...
than Gtk/Qt but still looks half decent.