But I couldn't achieve the same result with the Vestals and archers of the Order faction on day 5, even on a normal difficulty level. Healing, restoration, magic, and other abilities didn't help.
Therefore, a counter-question: How can the Order faction advance without losses at the beginning?

Surprisingly, I only managed to win all battles with the Order faction without losses at the very beginning, practically against all neutral creatures. The main problems were with ranged neutral creatures. I don't focus too much on hero development; I try to stick to the main directions: mage - magical skills, warrior - strength, and accordingly, skills of the Path of Blood and Tears. And the order of battles is approximately as follows: I wait for the enemy on my territory, attacking with crossbowmen, Vestals, or healing if the corresponding neutral creatures are present; I attack from a distance with the same ability if there are griffons, then I always attack from the sky on the first turn; if the griffons are advanced, then I can hit several units at once. And the guards finish them off.