Yes, reliability. Systemd was the first mainstream init system to deal with service confinement via cgroups, service readiness protocols, and true event-based service activation.
To give you some perspective, at that time, upstart was using ptrace() to detect the double-forking to allow services to be tracked.
Tracking services doesn't provide for a reliable init system. From my perspective, the only job for init is to control startup and shutdown of services.
Not to keep them running. Not to restart them. Not to track them.
I have logs, and monitoring software for that. I have loads of applications to do that, if I wish. But regardless of what you believe an init system is for, the reliability of it is separate from "keeping apps that are so crappy they crash, running".
To give you some perspective, at that time, upstart was using ptrace() to detect the double-forking to allow services to be tracked.