Here's what chatgpt summarised for me after a bit of back and forth.

We don't have an "Authentication service" that issues and verifies a user's identity. We use nostr pubkeys for identity. I also think that we avoid the "participation privacy" issue that he mentions in the article but want to clarify what he means with him before claiming anything. 😉

Yes that's what I'm confused about. @SimpleX Chat identities are pubkeys too so what's the problem adopting MLS.