Re: "the system has a more modern and 'flatter' look"
@Hstubbe : "Multi-monitor support also sucks for both kde and gnome."
I don't know about gnome (haven't used it for 10 years) but Kwin (KDE Plasma 5.12) is clearly one of the best window/display managers. I have multiple screens, at work, at home, in conferences, HDMI, DisplayPort, DVI, and it all just works. I never need to reboot, uptimes are in weeks.
What needs do you have that Kwin doesn't do ?