You may want to look into getting a tiling plugin for KDE. I'm in pretty much the same boat as you, used to use tiling WMs but now on Arch + KDE. The KWin tiling plugins are fairly simple - the only configuration is setting shortcuts to move windows around and resize them (I use super+WASD to move between workspaces, super+ctrl+WASD to move windows around on the screen, super+alt+WASD to move windows between workspaces, and super+Q/E to resize windows). That's it - the plugins make using the computer easier in 95% of cases without adding too much complexity, for for the other 5% you just toggle off the tiling and do it manually. And of course the mouse is still usable to move/resize windows.
I currently use the Sticky Window Snapping[0] plug-in which allows resizing tiled windows together (see the demo at the link) and that does most of what I need. A lot of what I do now is fairly horrendous when attempted with a tiling window manager (music production with lots of vst windows open, using mouse heavy programs like Vivado and gimp), which soured me to tilers after using them for years.
I still have my treasured xmonad config available as an xsession for when i'm just doing dev things, and use it most of the time on the laptop I do programming with, but in general plasma5 is such a step up from any older versions of KDE it just works really nicely for everything else.
I'll have a look at the KDE tiling plugins although I'll be surprised if it can replace my xmonad setup (would be nice though).
Here's a newer script that overall seems to work better: https://github.com/lingtjien/Grid-Tiling-Kwin
And the older script I used to use: https://github.com/faho/kwin-tiling