Six products, each earning its complexity for one shape.
BigQuery is never a transactional backend, and vice versa.
ProductFits
FirestoreDocument-shaped app backends, real-time sync
BigtableMassive wide-column, time-series, IoT, ad-tech
BigQueryServerless analytics, ad hoc SQL, never live transactions
Spanner's global distribution + strong consistency has no truly direct AWS/Azure equivalent — a genuine GCP differentiator, not just a naming difference.