What we need are a force actually capable of standing off strategically (much less tactically) against the Deep Ones. The location of all their assets and military forces is really inconvenient to most of our force projection, and even if we can attack installations and wipe out forces by gathering PCs in strength that weakens us on other fronts significantly, and Varys' whole strategy counted on us gathering to attack them, meaning obviously Tiamat is ready and willing to try it too, and why wouldn't the Devils, who have been fighting the Deep Ones just as much as they have the Lannisters (if not more)?
We need enough military force from mercenaries or allies that we can split off a strike team of PCs but keep the other half ready to respond to any attack on our holdings, basically.
