I change between innate/bloodthorn/bloodspawn (Light high damage) and shackle/desert/valykn. (Heavy sustain build) 4x tristat, and running trifood/witchmothers. Damage comes from spell damage stone+all spell damage enchants. Aside from shackle maybe its pretty minmaxed. Heavy is OK, weaker than before, but has its uses in OW.
Best possible spread of sustain, damage and survival for current DK, 30k health, 15k mag, 37k mag. 3k buffed spell damage. Because battle roar+helping hands no longer scale, its not worth to just stack stam. More so regen. Health and mag are worth keeping high.
Yes, you trade cost reduction, penetration and regen for resistances, health and some stam sustain.
Generally speaking you're trading damage potential for survivability.
light armor is very viable on magdks, when you go for a lot of blocking, because the damage mitigation from heavy gets more and more diminishing, when you have other sources of mitigation and blocking gives a lot.