Quote Originally Posted by RichardButte View Post
1.5% for each of 8 people, which is a cumulative increase of 12%. If we want to call it 1.5%, we can, we just have to then divide AST's 1.5% by 8 to get the actual number since we're only casting that buff on one person instead of 8.
A cumulative increase in what? Certainly not damage.
Say you've got a four-man party where everyone's dealing 1000 DPS because that's convenient and also impossible. Your party deals:
1000 + 1000 + 1000 + 1000 = 4000 DPS

We've established that Fey Wind is (roughly) a 1.5% increase to each party member's DPS over the course of your fight.
This means each person's DPS rises to 1015, meaning it lets your party deal:
1015 + 1015 + 1015 + 1015 = 4060 DPS

How much of an increase is that?
4060 / 4000 = 1.015 -> 1.5%

So again, I see where you're pulling this '12%' from but it's ultimately meaningless. The only way to compare a single target Balance / Arrow to an AoE Balance/Arrow or Fey Wind is to know the exact DPS output of every party member - but again, single target DPS buffs are worthless in 8-man parties anyway.