Well after much trial and error, I only found one configuration that consistently works (mostly), and that's using KDE 5.8 which is brand-spankin'-new.
In addition to the distros mentioned in my question, I tried the following since then:
I tried OpenSuse just on a whim, and it's the only non-Debian based OS I even tried, I believe. At that point, I thought the others were broken because of a quirk in the Ubuntu/Debian base, until I stumbled across this blog post and realized that OpenSuse was using KDE v5.8!
At that point, i went on a mission to find an Ubuntu or Debian based distro that shipped with KDE 5.8, and that's when I found KDE Neon. So far I love it and it's quickly becoming my new fav (at least for a flashy/slick-desktop edition of Linux).
That blog post mentions "5.7 and beyond" as having this overhauled multi-monitor implementation, but I was having major issues with 5.7. 5.8 will occasionally give me hassles when docking, but it's never gotten to the point where I can't somehow finagle it into working without a reboot (and even better, without corrupting my whole WM/DM and reinstalling Linux!).
But with all that being said, I think it's clear that Linux has some catch-up to do in this arena. Not a single distro worked as well as Windows 8, 8.1, 10, etc does. Even the ones that do work (kinda), I can't say they worked without adding "(kinda)". They're tolerable, and usable, but hardly ideal.
Best Answer
Kubuntu makes many modifications to various applications (e.g., Firefox, OpenOffice), so it is unlikely that there is an easy way to recreate the Kubuntu look on ArchLinux.
That being said, I moved from Kubuntu to ArchLinux and I now prefer the vanilla applications (e.g., OpenOffice looks much better).
One thing that helped a lot in synchronizing the look of gtk applications with KDE was to install qtcurve, a theme that works for both qt (KDE) and gtk (Gnome) apps.