Yep, it works, I don't get any headaches from running it, so therefore it is OK.
I have started to look into the workings of systemd, and it certainly seems fine for modifying service dependencies, writing my own daemon, and customising the startup (though that is a rather ambiguous phrase). I can even use a sysv init script within a systemd service file, if I wanted to. You don't need to add debug output with systemd, because you don't need to write a script to start a daemon. It just starts the daemon you configure in a service file, and logs any output. That works for me, and to be honest, is actually much simpler.
Understanding bash syntax isn't as useful on HP-UX and FreeBSD. That shell isn't guaranteed to be available. A sysv init script isn't as portable as you make it out to be, because of inconsistencies between the different systems you mentioned. Good luck getting a Slackware init script to run on HP-UX. You _could_ make a portable script, I suppose. So that is an advantage, even if it takes extra work to properly test the script on every type of system you need to run it on. But if you have any Solaris SMF systems, portability goes down the drain.
Systemd is a change in the way thing run. It takes some adjusting and getting used to. If you make the effort, you'll find that you can make it work for what you want. That's an OK in my books.