How is BSD init not useful? All it's supposed to do it start and maybe stop services, and it does that quite well.

BSD init is pretty small and clean. I would argue systemd is much less so because of the large scope of the project. The more lines of code and features you have means there's going to be more bugs and more ugliness, and that's true for all large programs. New doesn't mean better either. If it isn't broken and still works well, then you don't need a replacement, which really is why systemd exists to begin with. Sysvinit was a god awful and byzantine program IMO.