I wasn't suggesting that the dialogue was directly crafted by the Gravemind; it's a possibility, but all I'm claiming here is that he was overseeing the conversation to put on a certain show for Arby and the Chief.

: The Arbiter didn't seem to
: think much of the exchange

Why wouldn't he? It's an argument between an Oracle and a prophet hierarch. Whether Arby suspected it was the Gravemind controlling the conversation directly, or thought that the characters themselves were speaking freely, he should have found it interesting.

And in the original cinematic (not so much the Blur version, which has some pretty nonsensical photography at this point), he's very clearly showing interest by the time the Gravemind gets to "...or all will perish as they did before."