Alternative Creatures - creature replacement.

What do you think about replacing Knights (level 6) with Angels, and Angels (level 7) with Light Dragons from Heroes of Might and Magic VII? By the way, why replace Devils with Ravagers if, according to the lore, Ravagers are even weaker than Cave Demons (which became Lords of the Abyss in Heroes of Might and Magic V), and Cave Demons are weaker than Devils?