To me it makes no logical sense to save Treviso. If Minrathous loses, your enemy gains all those military resources and strengthens your enemy significantly. If Treviso loses, your enemy gains a market town, which doesn't strengthen them much at all. Saving Minrathous is the right decision if your goal is to stop the gods and ensure that you don't lose the war. Saving Treviso instead of Minrathous is like saving some market town in Derby instead of London during WW2.