That was never the promise. The nearest to that is the promise of multi-cloud or hybrid infrastructure, but neither of those have anything to do with outages of specific Microsoft services.

The "you can't possibly have better redundancy in your on-prem" was absolutely a sales pitch I heard to move to Microsoft 365.

The biggest site I work for, who went M365 hybrid last year, has incurred more Exchange downtime today than they had all of last year with their on-prem Exchange servers.