Strange then, that so many people and particularly those who haven't spent years or decades fighting their OS or desktop environment, seem to disagree.

Every time a linux user says "everything just works" there's a massive gotcha. Remove the terminal and try to use a linux system, setting everything up, while properly roleplaying those who haven't spent years to get used to linux's many weird choices and you'll perhaps understand.

I've installed Ubuntu and Fedora KDE for less technical relatives and they've used them without issues.

Choices are only weird if there's prior experience with something else with significant enough differences. In this case I still remember the effort it took to switch from Windows to Linux, but I used Zorin OS to make that road smoother.

I suggest you try it now, I think you're stuck on outdated knowledge.