KDE4 was latter half of 00's. Oh, the bitter memories of having your CPU and memory getting hogged by the mysterious daemon called Akonadi. Or was it Nepomuk? At that time, many waved away concerns that Linux was simply using the unused memory for caching stuff, which is why the resource usage viewer displayed very small free memory amount, so they say. Well, that didn't explain the excessive swap thrashing that was occurring in the background.
Hunted for workarounds only to find out that disabling the above services also disables some essential desktop features, and made me rethink whether the switch from GNOME 3 was worth it. Sure, GNOME 3 had horrible UX, but at least my PC still had resources to do other stuffs then. But I sure missed GNOME 2 at that time.
Was it really, or was that just a rumor from non-technical "C++ is bloated" Linux crowd?
I used to run KDE in the early 00's, and it run just fine, in very primitive CPUs of the time.