Does Route53 depend on services in us-east-1 though? Or maybe it's something else, but i recall us-east-1 downtime causing service downtime for global services
Amazon calls this "static stability".
In this outage, my service (on GCP) had static stability, which was great. However, some other similar services failed, and we got more load, but we couldn't start additional instances to handle the load because of the outage, and so we had overloaded servers and poor service quality.
Mayhaps we could have adjusted load across regions to manage instance load, but that's not something we normally do.
The classic example is overprovisioning so that you can handle the extra zonal load in the event of a zonal outage without needing to scale up.