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 agree with you Icebreaker is my go to sniper when I run PvE solo. And it wrecks those -blam!-ing shielded shanks in nightfall