Also anecdotally, during the outage, test messages from my non-gmail account to my standalone/non-enterprise gmail accounts consistently bounced; test messages from my non-gmail account to my G Suite Business-associated account went through.

Serious question: how would you know that you are receiving ALL emails from ALL senders?

Totally valid, and I wouldn't. The status page indicates that "Google Workspaces" is affected, but I don't know if that is synonymous with what I have (which was Google Apps a decade ago, unsure now). All I can say is I was receiving emails during the affected window.