Who installed linux and did the initial setup? And then I think there is a class of user that is savvy enough to say, update their graphics drivers but not willing to use a terminal and that is before you get into the mess that is Nvidia on linux.
I agree, under a managed setup scenario where a user is only really going to use a web browser and a few apps. Linux is just fine.
I installed, she could do the same, insert USB stick, run the graphical installer, remove it, boot into the new OS. That's all I did, on this machine, our LR TV PC, MVR PC, DR PC (for pleasant visual videos on YouTube), her PC, etc. Some are Dell, some are Lenovo, my last PC was an HP. I personally have used nVidia on multiple machines and models the past 2 decades. On mid-2000's machines I'd sometimes have to run the driver installer .sh file I downloaded from their site. The past at least 10 years, it gets installed automatically, didn't have to do anything.
Glad we agree on casual users. She uses Chrome and only 2 apps, same as when she was on Windows. Would you agree that probably most of the world is made up of casual users?
My wife is the average computer user and has used Linux apps for years and never opened a terminal once.