There are other P2P transport alternatives, check out SSB's (it is really good!) or ours (gun.eco/docs/DAM) which prevents flooding. WebRTC and websocket implementations exist.
In any case, floodsub is just one option you can use for pubsub on top of libp2p (one with a notably high level of reliability and minimal cross network latency for infrequent messaging). We also have a tree pruning gossiping implementation called gossipsub. Take a look at the spec: https://github.com/libp2p/specs/blob/master/pubsub/gossipsub...
> The meshsub router offers a baseline construction with good amplification control properties, which we augment with gossip about message flow.
This is notoriously hard to get right. How to prevent spam, posioning or Sybils in your gossip network? Scientific work on p2p overlays and gossip is hard to publish now at venues like Usenix or NSDI. After Newscast from 2003 it seems you need strong identity to make these systems attack resilient. An unsolved problem.
Thank you for this insight! We will put a university student team on exploring this likely vulnerability in IPFS/libp2p.