As a 23 BH bodyguard I simply couldn't keep up with the healing (other members were 24).
We downed them after the two we killed on the third* attempt did not respawn. Mostly the same group ran Athiss with me at level 18.
Annoying that critical efficiency is a level 24 talent
I'm sure once I get it the fight will become much easier.
This fight made me really wish the heat metric was easier for other classes to measure by looking at my bar. I try to pop SCG at 30-35 heat to make the most of it, sometimes I'll tap zero a second before my next heal goes off.
"you're not healing you have no heat"
*first attempt saw me try to concussion the trooper which eventually led to the wipe since I had to burst heal to keep myself up when all but the sentinel focused on me (adrenal, supercharged gas, Vent heat, 1400hp from medpack, and shield), though I was naturally blamed.