you don't have to go light armor, i'm assuming you're still on heavy. health is a major palyer in PvP. i'm currently lvl 28 DK and I PvP frequently, switched from bow to destro staff at lvl 20. sword and board as my other weapon of course. Essentially, my PvP plan is start with destro staff, long range DPS, using chains and talons to manipulate enemies, then i have a staff skill and that fire slash ability for the healing and good damage over time. finish that bar up with coagulating blood for healing.

My other bar is a PvE bar, but is still highly effective in PvP. Fire whip for magic dump, ransack and low slash for taunt / enemy manipulation, stone fist for pissing people off in PvP and round that bar off with that spiked armor ability with the aoe morph for a small aoe with damage return and highly increased armor.