Honestly, I've been expecting this change for quite a while. It's the same issue with armor penetration. Although the armor scaling system is based on "time to live" rather than a linear scale, it still means that a given flat armor reduction for a cloth wearer is more significant in terms of additional damage taken per hit than the same amount on a plate wearer. Cross-reference that with the fact that PvP is about burst rather than sustained damage and you see the dilemma.
Consider this, Heart - the new Sunder Armor will be a lot more effective when you go toe to toe with, say, another Prot Warrior.