The gap is indeed the time, or the method of acquisition. For many players, Exotic gear is a short-term to mid-term goal. And the Legendary gear is intended as long-term goal (but we have found out that player absolutely want to get their "Legendary" as fast as possible - that's why we are making changes in this area). So after this change we will have the Exotic gear as short-term (direct) goal, the Ascended gear as mid-term goal (on the side, as it's not available as a complete set right from the start) and the Legendary gear as long term career goal for your hero.