What has been your experience scaling Firebase?

I did some stress-testing of Firebase today which left me quite pessimistic at the prospect of using it a a full-on mobile backend replacement. I added 100,000 fake user nodes (each with 10 child nodes), and while the query time for a single user remained constant (about 250ms) between 1000, 10000, and 100000 fake users, the bandwidth usage scaled to take up 10s of megabytes for each request once I reached the 100k mark. In the course of about an hour of testing, I had used 300mb of bandwidth (the Firebase free tier currently caps out at 10gb). I know firebase is supposed to be used more for realtime use cases (chat, real-time locations, etc.), but does anyone has any experience with using it as a replacement for a traditional (non-realtime) database?