Most settings applications (GNOME Settings, KDE Control Center) give very limited access to managing lower level components in the system. For example, kernel management, managing groups, etc.
If they did though, in your opinion, what would be the most effective way to offer a simple experience for some users, and more control for those who need it? How would most desktops implement this “hybrid” approach?
Or should users not be able to control those things graphically at all?
You guessed wrong. I speak here from experience that I have made with third parties but also myself.
In the two decades I’ve been using Linux myself, I’ve broken quite a few Linux installations because I played around with something in the terminal emulator that I had no or too little knowledge of.
If I now imagine that these but also other advanced settings would be possible in the Mandriva control center or in the control center of Plasma with a few clicks, I would have destroyed my installations much more often. From therefore I remain with my opinion. Some settings should not be made easily accessible in pre-installed standard tools. Especially since beginners often do not know how to undo these changes if there are problems. I also think that the developers of e.g. the System Settings of Plasma have already thought about why one only has the configuration options that the tool offers. And also a warning that is displayed when you start the advanced mode, for example, will not be useful. Nowadays, this will be often ignored.
And as already written, it is not so easy for some tools to offer a graphical interface at all. For example because they have a lot of parameters. Usually a GUI becomes so confusing in these cases that it is still easier to use them in the terminal emulator.