I thought the same way, but I think now Supabase is much better than Firebase. Simply because you get a lot more functionality from the postgresql DB compared to the nosql DB.
Fair I am not saying it is the only option. Parse was really neat before I ever heard of Firebase, Meta acquired them but at least they released it somewhat open source.
“Intended” according to whom? The firebase landing page makes a couple references to being scalable, but otherwise it doesn’t appear that using Firebase at a smaller scale is outside its intended scope at all.
What does “intended according to the technology” even mean? Just because software is built to scale up, doesn't mean that using it at a smaller scale goes against its intention.
Marketing copy aside, it's not as if the technical docs discourage people from using it for non-scale use cases.
The scalability argument does not fly with me. Realtime Database is not scalable, and you will eventually need to use sharding to get it to work with reasonable amounts of data. Cloud Firestore is designed to extract as much money from you based on the structure of their pricing model - you are compelled to make unnecessary reads and duplicated writes in order to make comparable operations. If you want a scalable Nosql, why wouldn't you go for something like mongoDB cloud, which is far less likely to burn your startup's pockets?
The most definitive use case for Firebase is its Realtime capability, which makes it useful for gaming particularly but also team-based apps. But Supabase is just getting started with their Realtime capability - I expect to see more progress from them while Firebase deteriorates under the cloud of Google (pun intended).
Core competencies of most game devs aren't web stacks. I can see how web devs might feel differently.