It's the Biotic version of Carnage meaning useless in most cases.
It's nothing like carnage.
I think they simply wanted to keep it Aria-only, or at least they didn't want to create an appropriate kit to be able to use it. Not just any asari should be able to use Aria's signature power, after all.
They probably gave us DS to give us something Flare-like, and in some ways it's much better. Unfortunately, DS has a ton of off-host issues that Flare would not have had.. I would have liked to have both, personally.