Also, from what I can tell, OpenRC's 'supervise-daemon' resolves the problem folks claim to have with PID files. [0] While the PID file is still needed, the contents of that PID file is the PID of the supervise-daemon instance that's monitoring the service.

You might quite reasonably ask "What happens when supervise-daemon crashes or is OOM killed?". I would reply "I'd imagine the same thing that happens when 'systemd' crashes or is OOM killed, except with a far smaller circle of devastation.". I'd also expect supervise-daemon to be no less reliable than 'systemd'.

[0] I would also expect most service supervision systems to solve this problem. OpenRC has supported using s6 as a supervisor for a long time, and OpenRC's supervise-daemon is relatively new, seeing as how it was introduced in 2016. My comments are about supervise-daemon because that's the only one that I've bothered to use.