I think comparing destiny to defiance is dumb. Im guessing the weapons in defiance don't really scale with leveling, or the sole thing that makes weapons in defiance better is the amount of damage that it can do. Weapons in destiny are much different. Exotics are exotics because of the abilities they give. Invisible while zoomed in, increase health regeneration speed, being able to pick up ammo by shooting it, deploying entries at the site of explosion. All primary weapons will have similar kill times, snipers will similar, etc. It won't be like this common sniper won't kill in 2 hits. The differences will be miniscule, or leveling up a common will make those differences miniscule. A common rocket launcher will still kill an enemy in one hit, a more rare rocket launcher might have a bigger area of splash damage, or a bigger clip or something along those lines. That is my guess. So yes, someone with a exotic will be more (for lack of better words) powerful, but someone with a common weapon will still be able to win encounters.