This will change once we have our own OOBE setup for KDE Plasma. For
now, we don't have it, so we're at the mercy of what the user sets
during installation.
Not really. Workstation can set their own rules in anaconda, you can too. I believe it wouldn't be that much work to force creation of a regular user either in anaconda or in the initial setup. Furthermore, if you say you want it, we can have a release criterion saying that desktop environments must have a regular user account created. Our current criteria are weaker, but they can be changed, of course: