Remember: Tramennis was only promoted to Chief Warlord this morning. He may be a Warlord unit, but his specialty is clearly diplomacy, even when diplomacy isn't apparently the best option, or even possible. From http://www.erfworld.com/2010/10/book-2- ... dates-033/ :
One look at his scrawny frame, and Slately had sent him off to a far-flung campaign to the northeast, not much caring about the outcome.
Tramennis had neither conquered nor fallen on that mission, but had cornered the enemy and opted to negotiate. He returned with a new alliance, including quite a nice little tribute from the former enemy side.
What do we learn from this? Tramennis is a canny general, indeed so, but even when he finds himself in a position of strength ("cornered the enemy") he prefers diplomacy and negotiation over outright slaughter. Him choosing to negotiate in this situation, where to the best of his knowledge he's got GK by the short hairs, them being utterly unable to escape or do any significant damage, is completely within his character. It might not be the tactically best solution, but it's what he would do. He sees the opening salvo of Parson's plan, and does he consider it an attack? No, he immediately interprets it in a diplomatic context. Tramennis isn't thinking "What military use could doing this have?" but "What is he trying to communicate to me through this action?"
Besides, for all of his intelligence, Tramennis is a Royal, with everything that entails. He's very smart, but he's constrained to the same paradigms as the rest of the ruling class. His conversation with Ossomer betrays his notion that he truly does see Royalty as above non-Royals like Stanley. (Perhaps.)