You can install a sysvinit based stock debian if you wish. I've done it a few times recently, on low memory systems (<512MB) it does make a noticeable difference. It's mostly supported in terms of running, though the install is a bit manual:

https://wiki.debian.org/Init

There's also instructions for converting a running system, but I've had no luck with that. It just resulted in an unbootable system for me as it couldn't fully remove systemd there.