Here's the API reference if you'd like details [1]. They are very much not just standard Linux permissions. Android includes a huge set of APIs on top of Linux
[1] https://developer.android.com/reference/android/Manifest.per...
KDE and Gnome are desktop environments that runs on top of an OS, they themselves are categorically not OS, and they don't provide OS facilitates. They don't even directly talk to RAM or core hardware without an OS managing everything in the middle.
Android is all by itself an OS, it got everything an OS should have, scheduler/trap handling, runtime, system apis/syscalls all the good stuff. It's just happened that Android currently runs on top of Linux kernel, and it utilizes the kernel to provide some aforementioned facilitates, so yes you can say Android builds On Top of Linux, but that's not saying Android Is Linux, the sentences simply mean different things.
And it can only be archived with a fully locked down hardware?
Of course not. The modern OS archives system security through permission and isolation, which don't require bootlock etc to work. In fact, it worked well too even after the device is unlocked & rooted.
> Windows failed to deliver this; the average customer never downloads an Exe from a newer publisher without terror
Windows (and Linux for that matter) is not modern OS. They're classic OS that offers the entire computer as playground for the program running on top of it. That's why Windows can be contaminated with a single malice EXE, but not Android or iOS.
OSs are not the same, don't try get the water muddy that way.