build up 4 stacks of +5% devastate chance while saving power and avoiding any cast ability and trigger his fear + big heal(make sure addle debuff is on all the time). now you got 30s to burn down 12k morale to about 3-4k. twist + one full critchain with aimed fb = win.
btw those flies are a cast ability, there will be no flies if you addle correctly.
in a "normal" duel it's hard because in a duel you won't stun (ok in a duel you won't range-kite as a defiler, but ok)
I think a kiting defiler is the 2nd-hardes foe to a burg in a duel after a good warg these days together with a kiting weaver...