100% serious, look more into LXQT, or even KDE directly. The LXDE project supposedly is ended and QT is the new fork. But modern KDE, when everything is switched off, is lighter than almost anything else out there except for the lightest of light. Mind you: I use XFCE, but that's just cause I'm fussy. I'd use Cinnamon if it wasn't so buggy with alt tabbing in some games.
Yeah, I ran KDE for years. I believe im mostly on mate now but I have several systems so I don't always remember what I am using on them since I don't use them all daily.
Small correction: LXDE isn't dead, but the original crew moved over to the QT release. So depending on if you prefer GTK or QT desktop engine is the one you'd pick.