Not sure if I understand the graph approach. Do you mean somethingike a "Markov Chain" where redundancy leads to a lower probably of failure? 

Yes the metrics are an issue. If someone claims that nostr is a decentralized identity layer, I would strongly agree because it gives anyone with entropy an identity. However, I might disagree with claims that it's a decentralized transport layer because we rely heavily on ICANN and IANA to exchange notes.