Keep in mind Firebase has a big caveat. Firebase is great... for what it does. However, there's no way to easily migrate the Firebase resources to the larger GCP ecosystem. Firebase does what it does, and if you need anything else, you're out of luck.
Firebase is magic... but I never recommend it for anyone, until there's some sort of migration path.
[Firebaser here] that’s not quite accurate. For cloud functions they’re literally the same. Your Firebase function is actually a GCP function that you can manage behind the scenes.
With Cloud Firestore (our serverless DB) that’s the case as well. And Firebase Auth can be seamlessly upgraded to Google Cloud Identity Platform with a click.
However you’re right that for many Firebase products (Real-time Database, Hosting) there’s no relation to Cloud Resources.
Firebase is magic... but I never recommend it for anyone, until there's some sort of migration path.