I've come to a different way of thinking on this... Bungie is changing the meta to keep both game modes "fresh". It's the only thing that makes nerfing an entire weapon type anything close to sensible. Bungie has dropped hints to this several times in their notes, referring to giving each gun "their time in the sun". They also speak of "variety" and making other guns "viable". It's a forced rotation through their weapon set, and it forces you to play their content with multiple setups (thereby extending play on the thin content). So... don't blame PvP, IB, ToO, or any other PvP style of play. Bungie is doing this for their own reasons.