Evaluating archers.

But harpies – aren't they ranged attackers? Well, conditionally speaking. They attack, and then return to their original position.

A harpy isn't a ranged attacker. When attacking a unit with a Fire Shield, it will receive damage like any other melee unit.

+ Medusas often turn enemies to stone...

Often? Under my careful guidance, this happened 2 or 3 times throughout the entire game of Heroes. I suspect that they only turn enemies to stone in melee combat.