Isolation mechanisms is not what makes an OS. It's the stable ABI that application developers can depend on and which provides a way to use shared resources: disk, CPU, RAM, GPU, network, screen space, push notifications, GUI integrations, your favorite LLM integration, so on, so forth... Yes, it might have an imperfect security model, but nothing's perfect under the sun.
Raw Linux without userspace could be considered an OS, but it has the ABI only in form of syscalls and the minimal standard FS. That's barely enough for anything other than, say, a statically linked Go binary, which is why it's seldom used by app developers as a target.
To most of your examples I say – yes, that's an OS, and jails or zones have nothing to do with it. Although I'm not familiar with them other than FreeBSD, so I'm relying on your short description and your implied criteria for selecting these examples.
Raw Linux without userspace could be considered an OS, but it has the ABI only in form of syscalls and the minimal standard FS. That's barely enough for anything other than, say, a statically linked Go binary, which is why it's seldom used by app developers as a target.
To most of your examples I say – yes, that's an OS, and jails or zones have nothing to do with it. Although I'm not familiar with them other than FreeBSD, so I'm relying on your short description and your implied criteria for selecting these examples.