That's false: systemd handles a separate /usr just fine. It prints a warning, because most systems don't support a separate /usr partition reliably, no matter

That's false: systemd handles a separate /usr just fine. It prints a warning, because most systems don't support a separate /usr partition reliably, no matter which /sbin/init they use. Consider udev scripts that rely on binaries or libraries from /usr and are triggered on hardware cold plug events, before /usr is mounted: poof, some of your hardware magically doesn't work on boot, until you re-plug. Have fun debugging it.