I was leveling up Mokko (Hero (Strength) of the Stronghold faction) like this: education, reinforcement 1, restoration, healing, harass, logistics, steal, training, aggressor 1, 2, endurance 1, 2. In total, on the 5th day, at the normal difficulty level in the Broken Alliance, she could defeat around 50-65 neutral creatures without any losses (I don't remember the exact numbers). Tactics: Mokko, hall of heroes, 2nd hero, army doubling, stone of enlightenment, traps, reinforcements, harass, restoration. I haven't tried this on the difficult level yet.

But I couldn't do the same with vestals and archers of the Haven faction on the 5th day, but on the difficult level. Healing, restoration, magic, and everything else didn't help.
Therefore, a counter-question: How can I progress without losses at the start with the Haven faction?