Well, the very distro-specific bunch of scripts in /etc/init.d (or is it /etc/rc.d/init.d/? or /etc/rc.d? or a symlink to ...?) were some kind of tight coupling, too.

Plus: This tight coupling did not exactly replace existing communication features. It created new ones. These are made use of.

Yes, systemd is bringing lots of new functionality. Under the hood - that is why sysadmins love or loathe it and users mostly don't care. That "tight integration" argument is mostly one that comes from people (please do not take offence, you're weighting it carefully indeed!) who bemoan that other userspace system infrastructure is left behind feature-wise. And those who love to argue about and against design decisions.