The hollow operative seems painfully hard, even with the resonance thing. It charges too slow to be useful so I just end up dying. I put the medkit on autocast but it doesn't help. :<
Oh, you mean the Task Force, the final opponent of Area 6? My best strategy has been to try and kill them without ever giving them a chance to reinforce. To me, it feels like the reinforcements are a penalty for not using the right kind of strategy.
I have a hint for that if you'd like: What causes them to request reinforcements, and how can you plan around it?