I defeated Shaka-Karokat playing as Sinithar, and at most, I had 2 Hydras left. My strategy against him: Meteorite once, and then I bombarded with Fireball. Of course, a lot depends on the magic luck, and plus you need to control the rage of the Orcs (it's good that Wyverns don't have rage).
Added after 10 minutes
Sorry for the naivety, Holy Paladin, but have you played as Dungeon against Stronghold in the late or ultimate game, at least against the AI? If so, please write what happened. And if not, you can suggest something.