On February 28th, 2017, S3 had issues in us-east-1, not globally. It just happens that most customers create their buckets in us-east-1. (It’s the default bucket creation region.)

Buckets creation/deletion is a global operation, namespaces are all global for it. When us-east-1 goes down, so does bucket creation. All other operations proceed merrily, but yeah as we see over and over again, whenever us-east-1 has an outage everything seems to shit the bed because they've built everything out in us-east-1. Hopefully us-east-2 is starting to eat in to that.

This is correct (or at least was a couple years ago).

Correct, but quite a few AWS services are built on S3, and some apparently weren't using buckets per region.

That only affected buckets on us-east-1.

I worked at a company that was highly dependent on us-east at the time. We survived. This is very different