After getting dark knight 60 and playing it for a while

[Hundred]

Again, not relevant in any real situation since you'll have a healer by your side who will keep eveybody up with a single spell.

It's exactly like the "Shield Oath/Grit is better than Defiance because the healing boost is only 20%". Yes, in theory, it's true, but in practice, both are the same.

And you also didn't take into account Abyssal Drain too, which is marvelous for fight with multiple targets.

Healing potency per second is only theorycraft from the start as you do not spam Self-heals in that fashion in the first place, it's straight looking at the raw data and saying DRK's "capability" is less because it objectively is, so it's erronous to put this as a Dark Niche because they can do it every 6s when they don't actually have the self-heal advantage. In an actual engagement tanks have more to do then just spam Soul eater/Storms Path from 100-0.

Abyssal Drains heal can be relevant in multi-target fights. Unfortunately most fights prioritize single-target relevancy where there self healing is less potent. Even still DA Abyssal Drain is 39% of your mana, so while it is a boon and Blood Price can extend your ability to utilize this, for general content its healing is often not capitalized on. You are certainly correct that Drk can be ahead for a moment with the skill but the useage is limited and if we're talking "relevant in any real situation since you'll have a healer by your side who will keep eveybody up with a single spell." It generally isn't relevant at all.

Players should really just consider it like this: Drk's 'strengths' are elsewhere