Aymeric strikes me as an individual trying to be as diplomatic as possible in the face of a series of crises. The Dravanian Conflict is his biggest concern, then there's the Primal threat and how it is directly linked with the heretics, the fact that the Garlean War of Succession is over and its armies could march on Eorzea very soon, and the potential threat of a revived Midgardsormr, which to Ishgard, is considered about as bad as a revived Bahamut would be to us.

From what I gathered, Aymeric's resources are limited and his influence even moreso, and despite that, he managed to keep his resolve quite well. While I wouldn't put trust into him (or anyone in the main cast, for that matter), I don't believe he wants to turn away an alliance. Just that his armies have bigger fish to fry at the moment. Though considering Shiva's appearance, that report may cause some minds to change, inevitably leading into the story for the Heavensward expansion.