Hrrm. That may still be the case, but on modern systems it doesn't really matter anymore. By modern systems I mean anything since about 2010 with enough RAM. On such systems, even end-of-life/support Intel Kaby Lake Core-I5/7(t(35Watt)) with 4 or 8 cores, and 32GB RAM I couldn't care less about Plasma(KDE), even when they are downclocked to 800Mhz mostly.

On more modern systems even less so.

I'd like to see a demonstration of that fastness, which translates into tangible usability benefits. Not some synthetic microbenchmarking shit.

I tried it, because I still know FVWM2. Was refreshing for a while, felt good because I still could 'do it', but that's it.

The only things I can imagine profiting from it would be running stuff which is at the limit for your physical RAM, where every wasted Megabyte decides between swapping to death, or running through smoothly. But then there is IceWM, which is good enough for such cases. With the exception of FVWMs excellent handling of large virtual desktops.