I would suggest to reduce the orcs' cost when recruiting them. The Orcs can stay be free, bu the Orc Pikemen could cost only 100 resources and the Orc Archers cost 200 resources. After all, the Mordor game style is spam a huge army of weak units at low cost. Making Orc Pikemen and Arches cost the same or more as other faction units defeats the reason Mordor's strategy of recruit troops with few resources.
The Orcs recruited in Minas Morgul/Dol Guldir/Cirith Ungol barrack can maintain the price, after all, they're updated orcs and are stronger than the basic recruited orcs.
Also you could rise the price for recruit Siege Weapons and Trolls balance the faction after of reduce the orc's prices.