DG5 nether research: why so hard?

So, I got the carnage nether research unlocked. And I did finally get a team through once, but they're regularly getting wiped out. They're all >1k level, they have a mix of pre-carnage and carnage gear, they all have Invader (and have it equipped)... What am I missing? Do I need to actually level up their armor and weapon masteries more?