Heavy Armour is OP.
Act 1 it completely sucks though, when it's just crappy 14 AC which is the same as medium armour like the Breastplate +1 or Githyanki Half Plate.
But once you get Adamantite Scale and some of the later heavy armours that get that +2 (Or +3 for the Hellplate) DR it becomes super strong.
+2 DR from heavy armour, +3 DR from Heavy Armour Mastery feat and Warding Bond and you take literally 0 damage from most attacks. AC is low? Who cares, hit me for 0 damage all you want.