So lately as I've been beefing up CLS I've been just straight up running them against Nihilus to see how the damage output compares. I get him down 3-4% with my team. R2 died round 7ish. Get down to 4 rounds or 3 left and his health is locked in at 68.8%
It isn't the protection recovery thing. My CLS usually wipes 80% of his protection with his unique attack. Nihilu's protection stopped going below 10% no matter what. Rest of the rounds went like that. Only thing I can figure was that the 2 stacks of confuse on him might have had something to do with it.