I don't want to minimize the impact from cognito and r53, but that's quite a different scale of failure than the OP implies. It's been a while since I used AWS, but we had multiple regions and saw no impact to our services in other regions the one time that us-east-1 had a major failure. And we used r53.

Perhaps I could've been more precise with my words. What I meant to say is IAM and r53 are two of many critical services that all depend on us-east-1. It goes without saying that if those services go down in us-east-1, the whole AWS is affected. This doesn't just happen "usually." When IAM goes down, AWS experiences major issues across all regions. If you were okay, perhaps you got lucky? Our team has 7 different prod regions and we see multiple regions go down every time a problem of this scale occurs.

If your product requires 100% uptime, you may need to look at backup options or design your product in such a way that can handle temporary cloud failures.