Having multiple vessels to flit between seemed to be vital in the metaphysics of how Shaeonanra avoided damnation. If he has a new vessel, he's probably still beset by this limitation. So rather than a single synthese vessel, it would be several, and he could only inhabit them in sequence. Which would likely make things awkward for combat.
Besides, Shaeonanra's real power is in his intellect. He's not the strongest sorcerer around, but the craftiest, the most creative, the least conventional. I'm sure he can do his best work in Golgotterath, not in the field.
That said, I'm sure that with their newfound mastery of the Tekne, the Consult has prepared some terrible surprises for the Ordeal. Plagues, weapon races, you name it. Perhaps we'll see some of them as soon as Dagliash.