Yes - I can see the point about them being mostly interested in crushing the rising church of Oronothor. And besides, once you have crushed the Ahma/Sela and whoever is supporting him militarily, destrying the rest of the faithful should be a child's task anyway. From this point of view, Eadric getting the fight "outside" makes perfect sense.
But are there any third powers on the continent/world? I was under the impression that the continent has 3 major areas - Wyre, Shuth and Nizkur, and that there's no other strong party. Of course, now we have the Adversary Reincarnated, and the immortals are very wary of angering him, but I don't see why he would could object to them slaughtering civilians - mainly because I don't seem him interested enough to care.
So, while I understand why Chesne's forces' goal is not to slaughter civilian population, it could nevertheless be a worthwile tactical gambit. Their summoned creatures cannot touch wyre's soil, without the Enforcer going after the asses of the summoners, but they could still send their all of their freaky amounts of undead and scatter them around. This would force Eadric to either stretch his forces to try and protect the civilians, or go with the ruthless route and try to make a push for hunting down the immortals as fast as possible and then going after the undead. The chesnite have no main base to protect - or rather, they do, but Kaalanaala can take care of her temple pretty well.
Just to make this clear - I am not criticising at all. I am pretty sure that it would make perfect sense if we were privy of all the info that Seb and his players have. But, that unfortunately not being possible, I am just discussing it (with the added benefit of a bump
)