Now thinking about it.. I do think there are a good space for a Dark Knight type of class.
I like the concept here. Very good work.
Would also attempt to add more hp/berserker type of theme in it as well. (in which HP would be part of your resource/power management)
So in a concept play.. could see something like...
First turn on an aura for passive effect. Toss a hold-charged curse spell to weaken your foe. (both could be at cost of your HP). Toss a Soul chain onto the foe, which make all damage to do redirected to the chained foe. Attack it with little regard for your hp, so as it gets low (like 25%) it would trigger something like a War Lust, which up your damage. Toss a Bloodsucking Chain on to the foe for both damaging and to stay alive. etc.