No offense but your table is kind of deceptive. Obviously you can route between anyone if your strategy is to fallback to using a proxy server. Libp2p do the same thing specifically for the same reason [simplistic code.] But the whole point of p2p networking is to not require one. The reason delta enumeration is important is because the information can allow you to support more restrictive NATs without needing a proxy server. It's more work to write the NAT code and more testing but it is worth it.
nope. it's not a fallback server, if you read our docs you'd see it's using another actual peer, but also many of the other cases are not routable in other libraries such as libp2p (which does fall back to servers in most cases).
and our NAT traversal success rate is comprehensive, every known routable path actually works (check this table https://socketsupply.co/blog/the-next-chapter-in-the-story-o...)
we're actually not reinventing too many wheels here, our work is conceptually based on DTNs — cited frequently in our guides and docs.