Wyverns

Yes, perhaps. But playing as Shaka isn't the best option, even if the game drags on; it's better to focus on Goshak.

Or, if you have to play against an aggressive faction (like Sylvan, for example), you can also choose Dark units because you'll likely have to play defensively, and you won't have time to focus on consuming units.

Playing Orcs defensively? That seems strange. I understand that battles can be diverse, but the strength of the Orcs lies in their speed on the battlefield. I can understand playing defensively with Dungeon (although they are also an aggressive faction), but defending with Orcs seems nonsensical to me.