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.
Maybe not where you are but that's legitimately what our project managers were saying. We all knew better, of course.
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.