With all possible respect, I've seen the comparison between weapon obsolescence is Destiny and in other games like WoW or Diablo a couple of times now, and its not entirely valid. Whereas in those other games the weapon (for the most part) is providing damage output and stat bonuses, in the Destiny the behavior perks on your weapons are your most used "skills". Imagine if your Rogue could only use Fan of Knives or your Warrior could only Sunder Armor while they had a specific weapon equipped. Then imagine that with the next expansion you were forced to give up those skills in favor of inferior ones only because of the damage stats on the weapon. The communities surrounding those games would no doubt be having this very same debate. The solution is to let us "learn" perks like Arc Damage and Firefly, and then let us either equip them or build them into our new weapons. Then players would feel like they were actually progressing when they replaced Fatebringer with that new Hand Cannon, and the controversy would evaporate.