From my testing, the performance characteristics of ets isn't that great - data still gets copied around when you access stuff in it. I tried using it in my exploratory tests and certain worst case, player-focused actions would take around 20ms, when using a regular GenServer with a synchronization system on top would take around 5us.

To be clear, for NPCs it worked fine. But players are hoarders and in an RPG that can result in a ridiculous amount of data being attached to them.