Unchained is very good for openers especially for Demon wall, Unchained + all offensive cd's till its done then get out of Defiance for pure boss burn. That being said I generally save Unchained for Burst moments like in T4 when we kill the first and last dreadnought because the emnity buff that the tanks have is just so op I find myself using one flash followed my one Overpower then go into my combos.