Dragons are not interested in being dragged into the conflicts of man. Without a direct threat to their interests/territory, they're not going to get involved.
It makes more sense to turn to the "human" expert first.
Especially when that human expert was actually merged with the Shade of Nidhogg for some time. Lunar Bahamut appears to be more egi-like than dragon-like (appears to obey Fandaniel's will as an example). Estinien's personal experience with both dragon and primal aspects could give him better insight.
If we did need to turn to the dragons for information, Tiamat would be a better choice as consort of Bahamut and party to the Ascians reviving him as a primal. I'm actually hoping she is involved in the story at some point.
Midgardsormr is basically in a state of hibernation. He's unlikely to awaken unless there is a threat to whatever Hydaelyn charged him to protect.