I thought 1 turn represented 1 month... (early/mid/late spring/summer/fall/winter = 3*4 =12)
Otherwise, I pretty much agree with you. For Caelum, I think buffing PD up a bit and making false horrors not spammable for a long time without severe fatique would be enough - it's not their military strength that people are worried about. If something needs to be done, maybe a magical net (NN, Hunter's net, supply bonus + 'lost wing' affliction for those hit, dmg 0 + entangle in AOE 1).
About devils, I think boosting up their classical counterpart, the angels, would deal with them quite nicely. If a small group of angels was able to devastate devils as well as small group of them is able to devastate independents...