The description may be misleading: The "armor bonus" is not an increase of 200%, but an increase to 200%, i.e. doubled armor rating rather than tripled. Further, the doubled armor rating only remains for 4 seconds, the duration of War Cry's Taunt effect, and gradually tapering back down to the default armor rating over the final 6 seconds of the ability's duration
Like most offensive abilities in the game, if War Cry doesn't hit any enemies, it does not trigger a cooldown and doesn't cost anything. Because of this, it is possible to spam the ability up to a point where the armor bonus stacks up to 9999 armor rating, before engaging in combat. An unofficial fix for pcis available here.