“Alternative League” is a mod that replaces the Dungeon faction.

Exactly. Prophets have terribly low damage against a single target but high damage against groups and tightly packed formations, practically without retaliation. They are complete garbage when attacking unit by unit, but Flame of Vengeance is a counter ability to imprisonment. As stated in the description, Prophets deal their damage to a target. Once again, they deal this damage to everyone if they are moving. And once again, they deal double damage to everyone around the target, excluding the target itself, which constitutes their real damage. As strange as it may sound, the target for the attack should not be the enemy's priority units.