It's been a while since I last leveled an Inquisitor, but going off what I do remember, I don't believe binding Kallig would have helped with the sickness. He might have been able to keep the other spirits in line, so to speak, but in the end he'd simply be another powerful spirit that Nox, without the measures taken on Belsavis and Voss, wouldn't be able to contain for long. Nox's problem was just as much that their body was unable to withstand housing such power indefinitely as it was that the spirits were intentionally messing with him/her.