For the curious, the endpoint itself is fast mostly because it's heavily implemented with Redis. Are you interested in a writeup of how that works? If so, leave a comment and I'll consider spinning that up.
Also, why don't you do the recursive lookup internally instead of having bundler do several calls? It seems like performance would be strictly better because it saves network round trips.
I could definitely see future iterations going down more levels and caching the result as well. Right now each dependency lookup is not cached, so that might cause issues once 1.1 is actually released :)