You are right - every single reward drop is about luck. However, never before has a quest been dependent on a specific thing being acquired from a specific adventure reward drop. (Plus don't forget this is compounded by the 2 week time limit so that a limitless number of adventures cannot be done.) The luck aspect IS new to completing quests - and it's a bad idea.
Also, don't forget that not everyone will have checked the forums and seen the full list of quests ahead of them. Think how those people will/do feel when they've already committed a lot of time and resources to the quest and only then find out that it's random as to whether they will be able to succeed. In your example the player knows at the start what they are letting themselves in for, but with Four Winds it is highly likely (particularly at the start of the event) that they had no idea of this and therefore will feel frustrated and a little cheated that they spent time and resources on it.