But the point is you are relying on that library truely doing nothing for evermore across upgrade after upgrade, until the day comes where libsystemd0 or whatever it is called depends itself on the systemd library, boom next upgrade you have systemd.
This happened a few times during devuan developement with reports from the alpha releases (and earlier) of 'i've used devuan sources, upgraded package such and such which has nothing to do with init and ended up with systemd again'
One of these was just due to the package including a service file for systemd but not including any calls to systemd, it therefore required systemd, for that one file to be interpreted, which was not used if systemd wasn't installed, but you ended up with systemd init as a result. It is abuse of the dependancy system, and lazy compiling of the upstream sources. The talk that you could use debian with sysvinit was nonsense when people actually tried.
Sometimes the answer was simple:
A compile time switch removed the dependancy on the 'do nothing' library. That in some cases was the only change from debian package to a devuan package. No need to change or patch the source itself.
In other cases there were actual uses of systemd api that was not necessary for the software to actually run so further source changes needed to be made to convert from a debian package to a devuan package.
Other packages (gnome et al). have been so integrated with systemd that it would be huge task to unpick.
'Well tested code' is not equal to 'used a lot cause it's there code'.
Dbus was not required for iptables to function. It is the package maintainers that make the decision that it should be included, but it is an unnecessary dependancy, UNLESS you want to use dbus to access iptables. i.e. feature creap, at the package level.
I have used iptables from the command line for donkeys years (since ipchains). And it worked. I never once thought, 'I know, I want to modify my iptables by installing X and gnome and some firewall editing GUI, to save a config file in some unknown format , so that some other service daemon can read my config file at boot and then use dbus to set the iptables rules'.
I can set the rules in an init file calling the commands directly and it's done.