Dumbest ability currently in the game. DW Frost DK's can basically get 60k-100k heals off of one Death Siphon which only costs one Death Rune. It's hardly a resource penalty for DW as Death Siphon generates runic power that can be used to mash Frost Strike which is DW's hardest hitting attack.
It's almost impossible to kill a DW Frost DK with a brain that knows how to abuse Blood Tap/Death Siphon/Plague Leech combo in conjunction with Pillar of Frost to make the heals even stronger as Death Siphon heals based on the amount of damage you deal to the target. This is only going to get worse as the season goes on when DW Frost DK's get full gear with full Mastery. Mastery stacking is the source as to why Death Siphon heals so much for DW. Death Siphon is shadowfrost damage much like BoS, Necrotic Plague is where the more Mastery you have, the stronger these abilities are.
The solution is that they should either nerf the damage Death Siphon deals by 30% or make it so that it doesn't generate runic power anymore. It's actually insane how hard it is to kill a DK where even if you have his/her healer locked out for 12 seconds straight and you severely outplay the shit out of them, the DK can just go into livelord mode with Death Siphon and live through whatever damage you throw at him/her.
People will argue that Death Siphon is counterable if you silence, stun, fear the DK. That argument would work for a normal class but not for DK's as DK's have 3 ways to stop stuns, 2 ways to stop silences and 2 ways to stop fears and on top of all of that anti magic shell.
I understand that DK's are a horribly designed trash tier no skilled class however, I want this dumb Death Siphon livelord shit to go away. It's not fun for anyone at all levels of the game from casual bg's to hardcore arena.