For whatever it’s worth, I use (up until fairly recently) KDE Plasma on Arch, and it’s pretty much fine. There’s some hiccups especially after a big update such as KDE Plasma 6, but it’s a smooth ride so far.

If the KDE Plasma developers support an Arch-based distro of their own, and package stuff for this distro with care, I think it’d be a better experience, but I am guessing not by much compared to KDE Plasma on base Arch.