Balance in Heroes 5.

I agree, on XL maps, Inferno (with an upgraded Call of Urgash) can, due to its high initiative and troop speed, and summoning reinforcements through portals, be the only faction that can truly stand against Necropolis with its thousands of skeleton archers.

Knights in versions 1.0-1.41 can also do it. They can have almost as many crossbowmen as Necropolis has skeleton archers. Especially if there are farms near the castle. And it's better not to let demons develop to the point of having the Call of Urgash. Otherwise, it will be difficult to deal with them.