Both traits also used by armored fighters + the advantages of discipline and armor. By all logic barbarians should be glass cannons and their rage should be more of a I kill you now before you kill me mode than a super thoughness mode.I understand where you're coming from, but in the abstract combat system of D&D where armor and hit points are not realistic, logical elements, it makes perfect sense. The Unarmored Defense of the barbarian is based off of Dex (dodging) and Con (shrugging off hits).
Why play a barbarian at all when he in play is more like a heavily armored knight than a barbarian?