[bravetraveler]

Not entirely, for example:

Units can depend on networking managed outside of systemd-networkd using the target -- think of this as a 'run level'

Units can depend on mounts outside of systemd .mount units -- there's a generator that considers fstab

At a certain point, you might want to go further into systemd... but it doesn't require it.

The basic 'this service wants/needs these other ones' is very self-contained, and inherits a lot.