After all, we will spend most of our mana on neutral creatures, and mana wells are not frequent, so we may run out of mana and lose many of our units, and what if an enemy hero appears?
Therefore, I think Protection would be a very useful skill in combination with Leadership + Light Magic (and to some extent, Chaos), if we quickly level it up to readiness (level 7), then there will be no problems with defeating neutral creatures, and the army enhancement skill will also go well with the direction of Light Magic. BUT then we must force the enemy to attack, and since we don't have Chaos magic, this will not be an easy task.
However, if we take two Priest upgrades at the same time, this problem is significantly reduced; we will use them not in the usual way (Mark + Fireball).
The main mass of Priests will use Fireballs, and the second upgrade is needed to create a wall behind the enemy, which will simply force them to attack. I think the strength of the Priests will be enough for the enemy to understand that they cannot sit in defense.