The problem with picking Night Fae as FDK is in order to maximize it you have to stand in D&D, you have to have another GCD before you can start dpsing, so more ramp up, then you have to worry about movement and timing of it.
So if you look at Patchwerk sims of it, I'm sure it beats out Kyrian. But in reality, Kyrian is an instant 40 yard DoT that doesn't punish you for using it first that can cleave onto other targets even when things happen to be getting repositioned. You don't see this on sims, this is an experience and knowledge type of thing.
Night Fae is basically a noob trap in raids unless you know all the fights and/or have them all on farm. But I'd wager a gamble that most people are selecting based on dungeons dps. The little critter teleport thing isn't as useful in dungeons as it is raids and Death's Due isn't as useful in raids/pvp as it is in dungeons.