you mean leave deviantart? Nah man... it's the only
place where I can shamelessly clone mac and get away
with it

Kwin had a shadow plugin, was dropped and now kwin
styles paint the window shadows. Plasma windows/panels/whatever
aren't normal windows tho and does not get managed
by kwin. If plasma these days has some own shadows
system I'm unsure but some years ago when I still
used it it didn't. Then the shadows was painted in
the plasma theme. There however was some some panelshadow
plasmoid, but that was long ago.

I don't see anything ugly - except the oxygen theme
in the screenshot and seems to be working like expected.

I understand however that you'd like the shadow
to be under the window and not over it, I guess
you could try setting so windows go over/cover
panels and how that works for ya.

You discovered an option that allows your gfx card
to take vacations? What option are you talking about
exactly? This has nothing to do with the shadows
tho, that much I can tell ya.