What is the General Consensus?

[Shurrikhan]

That is nonsense.
A boss isn't going to use a tankbuster every 15 seconds. You don't need a 15s CD to handle a tankbuster.
How to recognize a tankbuster: Can you read? Is the name of the skill a tankbuster? There, you recognized all of the game's threatening tankbusters.

What will happen every 15 seconds? Mechanics. Mechanics that affect the entire party. Mechanics that The Blackest Night does literally nothing against.

But TBN isn't limited to its defensive value. It also offers you a GCD option (Bloodspiller) that deals 100 potency more than your second strongest option, only 40 potency short of DA on Souleater (with this gap decreased when comparing crits, especially if DAing Bloodspiller as well). As long as it's fully consumed, it still gives nearly the same potency as Dark Arts, but with a free shield atop it.

Heck, if you consider them the GCDs spent in terms of their place in or out of their combo chains, the potency increase can actually be as high as 160, a 20 potency advantage over a simple DA-SS or DA-SE.