Fates are big because they don't have queues. It is that simple. Most of my Fate parties are usually 7-8 dps and 0-1 healer and 0-1 tanks. You can't convert that to a dungeon group even if it gave instant level 50 on entering.

That is the crucial flaw of any MMO who attempts party role systems. And it is not solved by nerfing fate respawn times or increasing dungeon exp. No you'd need more drastic changes.

Things that either let us be 1 tank, 1 healer, 6 dps in dungeons, or something that lets us play as tank/healer but get exp on a DPS class. When you have made it possible for people to enter dungeons, THEN you may talk about adjusting exp to make sure people want to go where they CAN GO.