Rugatonn surely does not think that Abrogail can be unbrainwashed upon the spot; or if she's modeling Sevar accurately, knows that Sevar would not have sent Abrogail here in a persuadable state. And Abrogail knows that Aspexia Rugatonn cannot be turned from her own course; least of all could any debate move Gorthoklek.
What she is contesting, then, are the opinions of the high officials and palace Security wizards uneasily watching all this.
This handful of Chelish powers cannot decide any large military-civil conflict, they have not the numbers or combined potency. But they are informative; the next batch of Chelish powers might not arrive to any different opinion, if these few backed Abrogail here, or Rugatonn.
"Oh, you worry that Sevar's sworn guesses are wrong? You don't know Hell's truth yourself, but you know that an INT 29 ilani is making errors and in a particular direction? Fine enough, then, Gorthoklek is right there. He can give us his own oath about anything I say that happens to be false."