.........As for the long walks, it's done to give the AI a chance to focus on developing its capital city, because when it has many cities, it doesn't spend all its efforts on just one. And while you're wandering through the dungeon, the AI will at least have some time to prepare for the battle.
That's why you need to put a REALLY STRONG guard on the teleporters - either try to win (losing some of your troops) and teleport, or walk: D
