There were pros and cons, I get the annoyance with the binary vs text files.
But systemd booted faster than upstart, despite upstart was made for speed and systemd was made for being robust. The robustness of systemd however made it possible to make the ini process multithreaded and still work flawlessly, where old ini systems tend to have race conditions that make it near impossible.
systemd is more robust, faster and more flexible, so how it wasn’t great remains a mystery to me?