on primal you only read from a single relay, theirs. when you configure a relay its only for which relays you write to I believe. on damus the relay list are both the relays you read from and write to. some clients even go further and allow you to configure relays you write to and read from separately.

Is that is why there is a major lag for notifications to hit? I've been experimenting keeping Primal, Ditto and Coracle open in browser. Even thought I've been posting via Primal, I typically get notifications back on it in Ditto 1st, Coracle 2nd and Primal a distant 3rd.

Unrelated to you question: Be careful. Primal asks for you personal information, but that's a terrible practice for anything nostr and bitcoin related. So don't put any of that into the app. Better to try a different client.