Another daemon for managing control groups

Another daemon for managing control groups

it's less clear what the benefit is of multiple incompatible implementations of cgroup managament to me.

The requirement of a single manager for cgroups is coming from the kernel side, not from systemd. Since systemd makes very heavy use of cgroups for process management, it makes sense for systemd to be that manager in distributions that use it. Otherwise, you have the init system depending on another process to do a truly essential part of its job, which doesn't seem any simpler than having an integrated system.