It would be nice if most of Google ran off GCP, but alas, few marquee Google properties run on GCP. Ever notice how Google search, GMail, etc are usually just fine during a GCP outage?
Well this is just untrue. Read the docs. Gcp uses lots of the same infra as other Google services. The whole global load balancer infra is one and the same. Spanner is used by maps, Gmail etc. In fact, that's where the service spawned from.