The thing with Hayasdan is that you can use two strategies when it comes to what units to use.

One strategy is just what palmtree mentioned. using slingers and archers to weaken the enemy, then using low end spear armed infantry to keep the enemy at bay while your bodyguard units crush them from behind. This said, Hayasdan also has access to medium sword armed infantry "Srakir Martikner" They do well against all sorts of units except phalanx type infantry. I would allso like to mention using the noble infantry units "Aznvakan Tiknapah" now these units are on par with the best of the best infantry in the game. Their secondary weapon is a long sword with a high leathality. These units cause alot of damage.

The second startegy is using horse archers to win your battles. I for example use the steppe riders. These are the horse archers who have a spear that can muster a good charge. What I do is attack one phalanx unit from the back with one unit of the steppe riders, and when the unit turns around to meet the threath I unleash about 3-5 units of the steppe riders on to their rear. This simple strategy will break the most elite phalanx unit in the game.