A while ago (Either with Heavensward or one of the early 3.x patches), the drop rate for the items in the quests for the Zodiac Braves weapons was increased to 100%.

But the quest text still says

Quote Originally Posted by Quest Text
By completing a dungeon, there is a small chance that you will obtain the associated item.
That should probably be changed. The quests in question are: "Labor of Love", "A Treasured Mother", "A Ponze of Flesh" and "Method in his Malice".