No, it wouldn't devalue your exotics. Comparing an exotic to a legendary is a bad comparison. Exotic weapons have powerful, unique abilities that go a step further than Raid gear - that's why you can only have 1 equipped. An element does not compare to the poisonous DoT of Thorn or the Wolfpack Rounds of Gjallarhorn. Seriously, Gjallarhorn could have been void or heck, even KINETIC, and it STILL would have been the most powerful exotic weapon in Y1. The perk is what defines the weapon, not its elemental charge. As for your statement about the standard legendary gear: No, raid gear will no further "devalue" it than an exotic would. Thorn is a powerful Hand Cannon, but does it make Imago Loop less powerful? No, it doesn't. Feeling that legendaries are obsolete is solely up to YOU - the person. As the endgame gear of PvE, raid gear should outperform standard purple gear by a small margin - that's the reward/perk for finishing the hardest PvE content in the game.