Well, that's typically the beauty of sniper rifles as power weapons. They aren't easy, but their potential is huge. In the right hands, they can make someone nigh unstoppable. Bungie made them more abundant, but they also tuned up their relative power. LMGs and rockets absolutely do not do more damage, assuming a given sniper is regularly doing precision damage, which snipers benefit from a 5x multiplier on (no other gun class gets that kind of boost). With certain sniper rifles, Black Hammer, for instance, players can unleash an almost endless stream of this heavy, heavy damage. And they can do it from relative safety. If precision damage is taken out of the equation, sure, LMGs and rockets are a good way to go, but that's precisely the problem as is: we never have to choose between rockets or a sniper because we can carry both.