IMO supabase is not one to one mapping of firebase. Also this is one of a kind. Though it gives basic functionality of firebase like realtime update, database, auth, storage (only for cloud and not for self host) but there are some other stuff that firebase offers or you can do with firebase free of cost but here it is not available. I think people are migrating to supabase and not replacing it with firebase (just my hunch). Or the project scope covers supabase. But as a Postgres lover I think supabase has it's potential.