I disagree when you say that Atlas betrayed the witches by allying with the Demons. I say that because he never outright says that he will shield them completely (unless my memory is wrong). If I recall correctly, what he does promise is to spare the wich queen's sister (forgot her name) and to do what he can for her people so they don't get wiped out. He does that.
If it was up to Bael, he'd make the witches go extinct (as he wanted in the first place). When involving Lucius, the immunity for the witch queen's sister is honored, and the death toll on the witch population is then capped at a max of 50%. Which is still bad, surely, but less bad than total annihilation. If Atlas hadn't made a deal with the queen's sister, Lucius most likely would simply have assisted Bael without holding anything back.
