As someone that pen tests for a living I have to say you are very wrong. You said "The point is that nobody uses Kali to do actual work where you'd need KDE, Gnome, or Wayland. No matter what you read on some forums" Do you think that all pen test tools are run from the command line? Not so. There is a ton of tools on Kali which are GUI based and must be run from a desktop. Especially web hacking its hard to attack a site without a browser.
I do agree for the normal Linux user Kali is not a good choice. If you want to play around with Kali load it up on a USB and run it from there. Even using this method you will need a desktop to run a lot of the tools.
Still some of us that do this every day do run Kali as our default install. We add a normal user account for like writing on this forum and doing normal stuff and then login as root for testing only.
Setting up a normal user account and running Kali from there is no different than any other Debian install and just as secure.
KDE is known to break on Kali due to the KDE devs hardcoding root blocks and not using config files to block root access on normal Linux installs.
If you are going to use Kali best to use XFCE.
Yes I am an expert I have been doing this for over 20 years.