Armor is for real useless.

Playing in Lane against Yasuo as Gnar, all I found myself doing was, breaking his shield only for him to get it back and be taking no damage. I figured, well Gnar doesn't have enough damage output right now to kill Yasuo. So I decided to build armor, first item was a Wardens Mail. Yasuo, with just a stattik shiv, hits me with a single Q, and it did actually half my health. He hits me with his tornado under turret shortly after and ults me. Of course I die and he gets away with half health. How seriously useless is armor? Stacking health is out of the question too because the enemy just builds Botrk and Liandris.