Agreed, the hardcoded room is definitely not scalable to even larger numbers. Ideally, you would be able to shard the world, but I couldn’t find a good way to do that with the current exposed APIs in the short jam period we had.
Players are authoritative for their own state, but you are right that certain types of games need more server authoritative approaches (like League of Legends or Counterstrike). For a simple coop game like this, I think it is fine.