Some would say that the actual short CD is TBN and that's it's just as strong. And they'd be right that this is the skill that should be compared to HS, Blood and HoC, but it isn't as strong anymore.

I assume the idea would be that Oblation is a buff to TBN that you choose or not to apply so you can control wether or not TBN will pop from an attack. But it's honestly quite clunky and not that strong.

Personnaly I'd love for Oblation to be a TBN+ that turns it into a 25% Shield that reapplies after breaking, decreasing by 5% each time, granting several dark arts.
And while at it, make Shadowbringer Flood of Shadow upgraded when under dark arts. That'd likely work better.