It sounds like I missed something good there. Too bad I was taking one of my many breaks to play WoW at the time.
Well, most things in the Incarnate trials were +4 and had a lot of AoE. Before the devs addressed this, mastermind pets were -1 and -2 relative to the player. So your pets were facing +6s spamming AoE damage. This made most mastermind pets into instant roadkill.
Masterminds were, I think the polite word is "unhappy."
LOL thank you for reminding me!! I had totally forgotten about that meltdown. In the beginning really the only thing MM pets were good for was the Escapee part of the BAF- just plant them in a spot and set to Aggressive. (try using them on a Lamda and get the tissues ready, you'll be wailing very quickly) By the time the later trials rolled around it had gotten better, between Destiny powers, Hybrid powers and a shift in MM thinking from front line damage/tanking to back line damage & support.