This is the difference between “partitions” and “regions”. Partitions have fully separate IAM, DNS names, etc. This is how there are things like US Gov Cloud, the Chinese AWS cloud, and now the EU sovereign cloud
Yes, although unfortunately it’s not how AWS sold regions to customers. AWS folks consistently told customers that regions were independent and customers architected on that belief.
It was only when stuff started breaking that all this crap about “well actually stuff still relies on us-east-1” starts coming out.