Yes, you're right. I should rather say systemd makes administrating your system easier and gives you much more control. There's no reason to use old sysvint instead systemd or upstart.
Except that sysvinit is tried and true and well supported and well documented. Al ot Systemd implementations still have a lot of papercuts to overcome (like shutting down the network connection before NFS shares are unmounted for example). You also have to keep in mind that even through SteamOS is "hacker friendly" it is still targeted to towards a non-technical audience and as such the "administration" side of the equation is only a real concern to Valve and if they are comfortable with sysvinit then it really doesn't matter.