There is a mobile game I know of that had an outage as a result of a GCP service outage. That is the only time I've noticed GCP outages.

With that said, I would not say few companies rely on GCP. Search for "GCP" in this month's HN hiring thread. There are 23 hits, more than Azure's 21. AWS has 90 hits, which I guess shows its sheer dominance in the startup space. But these figures more or less agree with my intuition of the major clouds being AWS/GCP/Azure.