I actually posted something about this in another thread see in the linked post below. The key thing that I thought was relevant was a comparison between the DK’s Death Pact and a Warriors Bitter Immunity which are both talents in the same tier of the tree but what the Warrior talent provides vs the DK one shows clearly the disparate gap between talent power. The warrior talent has no negative residual effects and while it only is a 20% of Max health heal it also has the hugely beneficial effect of removing all Curses, Poisons and Diseases on a 3 Min Cooldown. Clearly this raises the question in relation to why does the DK talent have the negative healing absorb; if you think about this Death Pact is really only a 20% heal just like Bitter Immunity as the additional 30% that it does is effectively negated by the fact that it absorbs that amount in healing for 15 seconds which is a significant amount of time in any situation.
As mentioned in the post below my belief is that Death Pact should be modified to heal a flat amount with no negative impacts but instead provide additional benefits like the warriors talent. Consider Death Pact changing to provide something like a 20 - 30% heal of your Max health and additionally it also removes all Curses, Poisons and Bleeds on a 2 min or 3 min cooldown. The difference is that the warrior one removes Diseases while the DK version removes Bleeds; I feel the idea of having it remove bleeds is something that the DK needs in the toolkit as the other melee classes have a means to achieve this and the DK doesn’t have anything in their toolkit that provides this.
The reason I mentioned the 2 min to 3 min cooldown is essentially to balance the cooldown to be the same for both DK and Warrior so either the Warriors ability is reduced from a 3 min cooldown to a 2 min one to align it with Death Pact or Death Pact’s cooldown is increased to 3 min to align it with Bitter Immunity either way is acceptable however, most are going to want the 2 min cooldown obviously.