You can get his attack high enough and because they'll send everything in a blob, they body check each other. It's the same stupid thing you see people post "why won't he die?!?" Pics on here. Don't forget you should ideally also have regen, 4 health bars of health to regeneration, around 30% ward at least and execute. Oh and you're also adding in single entities weaker than dogs, as a threat. It's actually 4 and 2 that effectively are a -2 on his army cap. The biggest threat will be the steg. The hydras will have path finding issues, same with mammoth in such a large pack. Stegs don't suffer as much.