The systemd init isn't half an operating system any more than the coreutils "ls" utility is half a userspace. The systemd project has many different components but they're independent, they are not all literally part of the init system.
You're the one who brought up init systems. Like you said, systemd is a huge project; an init system is just one of its components.
> he systemd project has many different components but they're independent
They _are_ dependent. It's one codebas, and even if you somehow separated it - you would still only have systemd-specific, systemd-dependent replacements for _actual_ independent components.
They all depend on systemd and won't work with anything else, nor on any other operating system either.
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