Yeah, perhaps the healers and tanks must be forced to join a dungeon to let the DPS get through the story... sorry, yes its bad that the story requires a team to proceed but as most players insist on taking on the damage roles and leaving the others to other players, you will get this in every mmo... Tera online was the same, as a Mystic I got instances in seconds but DPS classes struggled, hell even in WoW as a Feral Druid Cat I had to wait for dungeons.