Well unlike destiny most MMO style games completely separate the two for good reason. Destiny seems like they attempted to do so but failed. You see, in other MMO style games PvP remains basically a different world than PvE. The reasoning is so that they can separately tweak one, or the other(which destiny has failed at doing). This eliminates problems that would come from say Nerfing the mytho, if PvP and PvE were seperate, then the Nerf associated with the mytho would have only applied to the PvP world. In that case the instant you step foot in an arena, the damage would be nerfed, but only when you're going into PvP. This would leave the mytho preforming normally for PvE. Where destiny went wrong with this I have no idea, considering all signs lead to them trying to keep them seperate.