@wink @rixx
Honestly since I switched to NixOS (btw)... Yeah.
But same could be said for Ansible or Chef or any kind of declarative infrastructure as code setup. Systemd timers have been rock solid for me. So, like you implied, the issue is not the timer but making sure the config survives. Good configuration hygiene goes a long way in mitigating this.
@ttamttam @wink likewise, most of my servers have been around for easily five years or more, and while I am far from a professional sysadmin, and I have broken many things, misplacing my systemd files has never been one of them.