Firebase is fantastic. There is also a steady drumbeat of continual improvements going on in Firebase that keeps making it better and better.

Even when Firebase is using other GCP products under the hood (e.g. Firebase Storage is Cloud Storage and Firebase Functions are Cloud Functions) they often provide a better developer experience that makes things flow smoother. For example, having a Firebase Function running on a schedule is a just an added line in your functions config whereas running a Cloud Function on a schedule requires setting up a Cloud Scheduler Job and linking everything together with PubSub.