OSs need to stop letting applications have a free reign of all the files on the file system by default. Some apps come with apparmor/selinux profiles and firejail is also a solution. But the UX needs to change.
Which operating system lets an application have "free reign of all the files on the file system by default"? Neither Linux, nor any BSD, nor MacOS, nor Windows does. For any of those I'd have to do something deliberately unsafe such as running it as a privileged account (which is not the "default").
I would argue the distinction between my own user and root is not meaningful when they say "all files by default".
As my own user, it can still access everything I can on a daily basis which is likely everything of importance. Sure it can't replace the sudo binary or something like that, but it doesn't matter because it's already too late.
Why when I download and run Firefox can it access every file my user can access, by default. Why couldn't it work a little closer to Android with an option for the user to open up more access. I think this is what they were getting at.
I'm not saying user files aren't important. What I am saying is the original poster was being hyperbolic and, while you say it's not important for your case, it is a meaningful distinction. In fact, that's why those operating systems do not allow that.