Yes, systemd not being a monolith is a myth.

You can forward logs to rsyslog or something, but you really can't disable systemd-journald. Technically you don't need to run systemd-boot, you can use grub or something else, but then bootctl and systemd kexec stop working. You don't need to run dbus, but if you don't several systemd features break, and it's not even documented what needs it. The list goes on and on.

Also, the fact that all components are in the same repository and need to be built together causes a lot of headaches with packaging due to dependency cycles (like, systemd -> cryptsetup -> lvm2 -> udev -> systemd).