Windows, VMS and some mainframes/micros have had such capabilities based file systems for years, it was not pioneered in mobile devices.

Now if some people just give access to everything instead of using ACLs, that is another matter.

Are you really any more secure after you make the initial mistake installing the app? It's not like an attacker is unaware of the security measures in place.

Well, I still lock the front door with the deadbolt at night although it won't stop a mob from breaking in, it's good enough to keep me reasonably safe against normal threats.

Also, actively circumvent protection devices is proof of malice and possibly even criminal intent (remember DMCA?) so I don't see your point.

Yes, because awareness does not automatically mean ability to circumvent.

Has there been any one year period in the last twenty years (NeXTSTEP for the first few years for MacOS) where there were not plentiful kernel exploits for Linux, MacOS, and Windows?

I don’t think so.