None of MeshCore, Meshtastic or Reticulum will scale well, especially not on top of a heavily constrained radio technology like LoRa. Flooding is inefficient for obvious reasons, AODV-esque routing (which MeshCore tries to do for DMs and Reticulum tries to do in general) is prone to almost-immediate path failure on unstable underlying transports, and the hidden node problem always bites on haphazard/unplanned mesh radio deployments where people show up with nodes in random locations on the same frequency.

The cracks are already extremely visible in MeshCore in the UK, where overheads from adverts and dropped packets from collisions mean it is already horrendously unreliable and most of the chatter in the Public channel is people sending test messages and being unsure whether anything they sent was ever heard by anyone.

Most other routing protocols (BATMAN included) are also not that well suited to situations where the underlying transport ends up asymmetric, e.g. one node can't hear others but it can be heard, and that's an extremely common occurrence/failure mode in wireless meshes like this. It's a difficult problem to solve with coordination between nodes, let alone without.