I can confirm that adding systemd.legacy_systemd_cgroup_controller in GRUB_CMDLINE_LINUX_DEFAULT inside /etc/default/grub effectively works around the issue.
systemd's Cgroup is infact mounted under cgroup hierarchy now: $ mount | grep systemd cgroup on /sys/fs/cgroup/systemd type cgroup (rw,nosuid,nodev,noexec,relatime,xattr,release_agent=/lib/systemd/systemd-cgroups-agent,name=systemd)
