WarKirby
Arty person
The PZ forces intelligent decisions.
Guess who's not capable of intelligent decisions?
The AI.
using pyre zombies against the AI is like giving yourself divine essence with the world builder. It's practically cheating, and they have no idea how to counteract it.
Aside from that, although it may force intelligent decisions on the part of someone playing against sheiam, it discourages intelligent decisions for the sheiam player. Because nothing is as effective as pyre zombie spam. You don't need any other tactics.
And if controlled by a human, the PZs are not so easy to outsmart. I always give mobility to mine, for a start. And I avoid tiles with roads, pilaging them where I find them.
Pyre zombies are extremely powerful because
1. The AI does not know how to exploit their weakness
2. A human player controlling them, can use them in a manner that negates their weakness, by giving them speed and avoiding roaded terrain.
One unit should have a simple rock/paper/scissors counter, because it's a simple tactic. Complex counter tactics should come when facing a complex mixed army. Pyre zombies force a disproportionate amount of effort and micromanagement on the part of their opponent, while almost negating the need for tactical thought by their user.