All major cloud platforms have occasional unplanned downtime. AWS had an outage last year that took many sites offline for hours. A single instance of Google having such unplanned downtime is meaningless without more datapoints.
As for whether it's useful for serious business. Well. Proof by example? This has sixteen pages of case studies: https://cloud.google.com/customers/. That is by no means all of GCP's serious customers.
As for whether it's useful for serious business. Well. Proof by example? This has sixteen pages of case studies: https://cloud.google.com/customers/. That is by no means all of GCP's serious customers.