As it stands this skill is outclassed by Magelight and Expert Hunter. Flames of Oblivion COULD have a use if hybrid builds were viable--but they aren't. Sea of Flames is a joke. The only builds using this skill were either 1) taking advantage of the bugged %20 cc tooltip or 2) Valkyn Skoria builds that were using it for the DoT (but they were also using Magelight for the +% magicka).
I suggest changing the skill to give DK class-based access to Major Brutality and Major Savagery, similar to Sorc's Surge (without the heal).
Invictus
Kilandros - Dragonknight / Grand Overlord
Deimos - Templar / Grand Warlord
Sias - Sorcerer / Prefect
Short answer is DKs likely won't be seeing a ton of changes before we go live; this class is still quite powerful (as it should be being a tank), even after some of the adjustments we've made to other classes and abilities.
DK IS NOT JUST A TANK CLASS. #PLAYTHEWAYYOUWANT