Static stability is a good start, but isn't enough.

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.