(I know nothing about cobbler. I just noticed its package requires /sbin/service and therefore initscripts-service).

But upstream commit 4fabc203550d1c450f94c5f96b2fe2aa66a13f35 ("add systemd and supervisord support", from 2021) did just that. As far as I can see the code always tries systemctl before trying /sbin/service. So, if I were a betting man, I'd bet the requirement for /sbin/service could be dropped (and one less package will be still dragging initscripts into installs).

If someone familiar with cobbler could test this that would be rather nice. Otherwise: is there more to this than installing cobbler, somehow disabling /sbin/service and then test starting and stopping with systemctl?

Reproducible: Didn't try