Isn't the plague applied to all of Benedict's units? When I tested the map, they all died within a few turns.
The plague was applied, but my units died first. I'll try again now.
Added 8 minutes later
I lost again. The reason: my archers always fail their morale check and never get to move. The plague doesn't affect Benedict's archers and monks because Benedict immediately gives them a blessing. Plus, these two and the ballista constantly get a morale bonus and often move. But that's just on the hero. At what level was the map tested?