But Double Flare comes out a whole lot faster than the DoTs and also F2 does good damage.
I think the key to SMN burst is by using the pet. Especially now that Aerial Slash is Instant. (Rouse+AS)
You can even have your Pet attack one mob while you attack another. Dots+Fester is decent burst and the Pet + Rouse is 140 Potency. So about 420 potency by the time SMN has 400 potency on a mob.