I'm afraid you are definitely out of the loop: Plasma is the DE. That is what it's called: Plasma, not KDE. KDE refers to the organisation, the community and all the software the community produces, which includes Plasma (the DE), but also all the apps, frameworks, widgets, etc.
I find it a bit ironic for KDE to be pushing this message, when it’s a heavy DE (relatively speaking)
You didn't seem to read my message. Allow me to repeat the gist here: Plasma (the DE) works fluidly on a machine bought in 2008 which comes with an Intel Core 2 Duo running at 1.8GHz. This machine has an onboard Intel GMA X3100 GPU and 2GB Memory. I doubt a heavy/bloated environment like you are imagining would even be able to display the log in screen on that.
I would advise you stop repeating third-hand FUD, as it is not true, and you tried the software out for yourself. I am sure you will be surprised at how light Plasma (the DE) is.