The more I think of it the more details I've editted into the list of what Eochaidh has to deal with right now...
I'm really trying to think of a reason to not withdraw because for gods sake, this ain't looking good for the expedition....
Actually, if you transpose this onto Star Wars, intelligence that a WMD giant beam canon exists is valuable in itself. Hence, making sure that someone escapes to report it is also a priority, and likewise the cultists may try to go for 100% rout (at the base camp - like in Rogue One) to ensure there are no survivors to report that the cultists have such a frightening weapon.
The monster attack at the base camp makes sense, although narratively speaking it would probably be more interesting if the camp sustained very high casualties.
From an RTS or chess perspective, if you move your main units to attack Cimon’s Hollow, it implies that the base camp would be less guarded. The ground attack doesn’t have to succeed as long as the enemy blockades Cimon’s Watch and prevents anyone from leaving. The allied faction notably does not have that many airships (aside from the Amarlys) now that the Getandmark fleet is incapacitated, so groups like Yew and the non-flyers could become trapped on Cimon’s Watch if the cultists managed to clean up the leftover and blockade/bombard the island.
Maybe some flying monsters would be interesting? Swarming Cimon’s Watch with overwhelming numbers of flying insect/plant monsters?
Anyways, I like disasters, so it’s more interesting to me when it’s a story about a defeat. Or well, I think beautiful strategy is beautiful, so I want to see something subarashi!