They can't make them better or preferable to other weapons, only more unique than other weapons. A mistake they made in vanilla was making all exotics unique and better than other weapons. If you had a VMC before it's original nerf, you were literally better at crucible, simply because it's TTK was inherently faster than all other primary weapons. If you had Gjallarhorn any time in year one, you were literally better at any PvE encounter. I think bungie overlooked this when they built destiny, and had to do a serious course correction in year two to keep people from dominating using weapons they only received by chance, and then proceed to use exclusively.