the release notes mention the “artwork”, but that is exactly what many people could not care less about. Just leave out all fancy stuff and give us a mono-colour desktop background. Everything else is just a distraction.
For many people a good looking interface with wallpapers is important, why would Apple sell so many of their OS otherwise 
Of course a lot has been done under the hood, just most people dont even notice or care about those “boring” stuff, as first thing they see is the “visuals”.
But I personally can understand your point, and also tend to use e.g. Core with a simple blue color like Windows2000 used to be.
same here. First thing is setting all things back to default. So currently: Default Breeze theme with a blue solid colour from Breeze screen lock/SDDM login as default DE background.
I may come across as an “artwork” hater, but here is why:
DO NOT USE THE “Air” design / Desktop Theme.
It will kill your install.
I posted this in 2017 and it still kills every KDE both in 2018 NRR as well as 2018 KaOS distro. :@
SOMEONE UPSTREAM must fix this “stuff” ideally by deleting the “Air” design of KDE.
here is how to reproduce: :dodgy:
in a pristine NRR-2018 installation, choose Air design and force font dpi downto 72dpi.
Your desktop will freeze and on reboot freeze again.
You must delete * in ~ and delete .* in ~ too
WTF ? :huh: :-/ :idea: 
:@ :dodgy:
actually “Air” itself works, but upon “screen notification” the TOTAL FREEZE will kill your install reproducibly. DAMN IT !! :@
Can anybody reproduce this? takes only 1 minute to find out. Pretty nasty bug.