The Ancient Horror is the only creature of level 7 that can defeat an Archangel in a one-on-one battle.

Well, if the Archangel is controlled by a clueless computer, then yes...
But if it's controlled by a human, the Ancient Horror has very little chance (I'm not ready to claim that it has no chance at all).

The Ancient Horror also shouldn't be stupid and should stand in the center of the map on its first turn.

Well, it also depends on the terrain... there are arenas where there is a large obstacle in the center, from one end of the field to the other. And if the field is clear... Then yes, I agree that to increase its already meager chances, the Ancient Horror should stand closer to the middle.