[Bu9818]

>namespaces (which have been a frequent source of vulnerabilities)...

Unprivileged user namespaces sure, but I don't think that applies to namespaces in general (which without unprivileged user namespaces can only be created by root, and LPE is the concern with unprivileged userns due to increased attack surface). systemd doesn't need unprivileged userns to run.