My thought was a teir 4 or national power would wield power enough to  influence whole nations, or kingdoms and be a major player within his own faction. Like a powerful Baron or other similar noble, who would easily command several hundred men. Where as 200 zombies, plus his other allies, would be sufficient to raze a small town or even a lightly manned fort. However any properly fortified city or castle would be untouchable. Besides, a heavy cavalry charge would be a very effective counter.

However I can reduce the number if need be.