AGI Gear Challenge - Issues defeating

I'm having issues defeating this challenge. Even at even tier 1. I'm team level 60 and have fairly strong characters. Granted this may be more do to my preconceived notions of how a challenge should work. Savage Opress uses an attack that drains a portion of her life and drains all of my characters life, but doesn't kill them. To be fair, I can then heal again, but it doesn't seem like any attack should be that powerful on a tier 1 against level 50+ characters. When I try tier 2, the droids are fast enough that they usually hit before I have a chance to heal and kill characters.

So far, by best strategy has been lots of healers and characters who can stun. The tips says to "utilize susceptibility". But I have yet to figure out what this is in reference to. Anyone else having similar issues or figure out good ways to beat this challenge?