Observability and operability are just not the same thing as being able to reason about the software. You need both

You can't capture the full range of behaviours and edge cases unless you are willing to ingest billions of events without lossiness

Metrics have limitations of cardinality. Logs need to be reduced or else you are in archive rehydration hell

There will be code paths that have never been triggered that you still need to reason about as part of analysing a system, eg in threat modelling

> I get why you think I might not have worked on large systems

I didn't, necessarily. But it looked like an excessively strong claim, combined with a challenge to the author's competence. I wanted to call that out.