But there is a huge difference (in my eyes) between fiddling with things that I want to change myself - because I would like the change - ... and not because I have to do the change in order for something TO WORK.
Fair enough. But this has a downside (I'll take drivers as an example) : You need to keep your system up to date. Namely the kernel. Having an OS isn't install & forget. I always make the comparison to cars which, from time to time have to be taken to the service and get fixed up. Now computers are much more versatile than cars, and hardware support doesn't magically happen. Hence maintaining a system that works out of the box with most things takes work.

(I still haven't found out how to make Ibus Chinese Pinyin input work properly in Kubuntu).
I had to google ibus...had no idea what that was. This brings me to market(developer) share : if there aren't devs that use it, it won't work...

In general I agree that things should "just work", but in the real world that is a nearly impossible task with hardware bugs/quirks, software bugs (an open-office specific hack in kwin comes to mind). Eg : When windows are spaced all wrong, you blame the window manager, but what if it is the app that's buggy? I believe that fullscreen unredirection should be and is enough (from my very limited testing), and any bugs were indeed the application's fault.