I agree with most of this but have to disagree about these shell scripts being slow. On Debian most of them were written for dash instead of bash and they were

I agree with most of this but have to disagree about these shell scripts being slow. On Debian most of them were written for dash instead of bash and they were executed in parallell based on magic comments which defined the dependencies. It was still a mess but a mess which was fast, not as fast as systemd but fast enough for most users. Additionally Upstart was not good. It has some good ideas but its approach to dependencies was generally regarded as unintuitive. Writing services in systemd is much more obvious than writing for Upstart.