Fusion with "instant" low-latency messaging?



We're looking into using Fusion and/or Realtime for our game. We are using a deterministic simulation and we synchronize inputs. The idea is to do lockstep and eventually rollback. We did look into quantum, but it's out of our price range.

We got the basics are working. However, using Fusion we don't control when network data is being sent and received (and RPC ordering issues). With Realtime it looks like we can, but then we don't have the state-based synchronization for the other parts of our game. I could not find a way to access the internals of the network layer to modify this behavior.

I would like to have the fusion-based approach for things like lobby (and some other aspects of our game), and the direct approach for our core gameplay, with unreliable/unordered messaging.

Is there a way to use both? Or should we stick to Realtime for this use case and manage the rest ourselves?