well here's the thing about gjallarhorn. It's exotic perk was basically just deal more damage. The weapon really didn't do anything unique or play any differently than a normal rocket launcher, it just did double damage. Now an ability like that is very overpowered for obvious reasons, but you can't simply nerf it or else the rocket launcher does nothing different than any tracking rocket launcher. The damage is the only thing that makes it special and that's really -blam!-ing hard to balance. Same goes for blink. Have you noticed that none of the new subclasses have blink? well that's because blink is fundamentally over powered as a short ranged teleport on your jump makes dodging a breeze even against supers and rockets, and it makes it so you can teleport in front of someone with a shotgun (completely ignoring any lack of range). You can't simply remove these things so the best thing Bungie can do is leave them behind in year one.