Sometimes discussions are important to really understand the impact of the proposal, though. I've been guilty of steering some reviews a bit off-topic trying to understand their impact. Even with the best intentions, it's sometimes hard to avoid.
Also, I don't get the impression that the core team merely does clerical work - sometimes they propose really different solutions to the original proposal, like the A & B existential syntax ([Returned for Revision] SE-0095: Replace protocol<P1, P2> syntax with Any<P1, P2>) or the \MyType.someProperty key-path syntax ([Returned for revision] SE-0161: Smart KeyPaths: Better Key-Value Coding for Swift).
That's maybe an argument for earlier involvement...