I don’t think it’s particularly relevant to this issue with fb. I suspect they didn’t need a monitoring system to know things were going badly.
- not arrogant - or complacent - haven't inadvertently acquired the company - know your tech peers well enough to have confidence in their identity during an emergency - do regular drills to simulate everything going wrong at once
Lots of us know what should be happening right now, but think back to the many situations we've all experienced where fallback systems turned into a nightmarish war story, then scale it up by 1000. This is a historic day, I think it's quite likely that the scale of the outage will lead to the breakup of the company because it's the Big One that people have been warning about for years.
The place where I worked had failure trees for every critical app and service. The goal for incident management was to triage and have an initial escalation for the right group within 15 minutes. When I left they were like 96% on target overall and 100% for infrastructure.