The Vault of Glass is still dropping the older versions of Exotic weapons. I hope that's an oversight in code, elsewise the incentive to continue fighting Atheon is boiled down to Ascendant material, which you can obtain on your own, without pulling together a group.
I picked up The Ice Breaker, and it was capped at 300 damage, after defeating Atheon on Hard. Please fix it at your earliest convenience.
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The vault of glass is nothing but a coding oversight. But I'm sure the VoG exotics are intended that way.