A "systemd like solution" LOL. Exactly ! As long at it's work as intended, perfect thing. But when you want to change, add or remove a thing you can't because it's far too complex tu use and really understand.
Mdadm and lvm2, both are doing a only thing but they did it well. Can't make differents raid level per file, yes. But at raid level you can do anything (reshaping, and so on)