I definitely don't agree with the decision to either arbitrarily or systematically leave certain exotics behind. With the introduction of blueprints to serve as a long term solution for clearing up space in vaults overcrowded by exotics it seems really counterintuitive. I can only guess that their logic here is similar to why previous endgame content isn't getting updated difficulties. They're thinking long term. If they keep their momentum and continue to build upon the preexisting Destiny world, in five years time there will be ten or more raids. That's an absurd amount of endgame content to grind across three characters. So certain weapons will be relevant for the content of their era, so to speak. And in the larger scheme of things, that totally makes sense, and I'm fine with that.