I don't recall Bungie showing off Gjallahorn before the base game launched. I assume, or rather hope, their mindset is just showing off some of the more marketable, pretty exotics to get people new to Destiny interested, and save the ones that will actually be exciting and game breaking for TTK. I also remember that they showed off Thorn in a Weekly Update a long time ago, and it was one of the worst guns in the game when it came out. I wouldn't jump to the conclusion that these are the best Bungie has to offer.