The protocol vs service distinction matters most where version lifecycles create lock-in. When you depend on a service, you're at the mercy of their deprecation timeline — Heroku free tier, Google Reader, Parse. When you depend on a protocol, the worst case is you switch implementations.

The identity point in the discussion is spot on. The missing piece in most protocol-first architectures is a portable identity layer that doesn't just recreate the service dependency at a different level. DIDs and Verifiable Credentials are trying to solve this but adoption is glacial because there's no compelling consumer use case yet — it's all enterprise compliance stuff.

The XMPP vs Matrix debate is interesting but somewhat misses the point. Both protocols work. The reason Discord won isn't protocol superiority — it's that they solved the 'empty room' problem by piggy-backing on gaming communities that already had social graphs. Protocol design is necessary but not sufficient; you also need a migration path that doesn't require everyone to switch simultaneously.