I honestly think that the Icebreaker is the most functional exotic to have in PvE Endgame content even if it isn't actually equipped more often than Gjallarhorn, because people use it to refill some of their Special ammo conveniently.
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I only ever use Gjallarhorn for Crota. Ever since the Bad Juju and Pulse Rifle buff, it's my go to Exotic for my Warlock. Nova bombs. Nova bombs everywhere...