I don't necessarily want to wade into the larger issues being debated back and forth here, but I don't agree with this portion of your post. I don't think the X^3 works as life 9 nearly as well as it works as life 6. Precisely because each of the lives that come after it are clearly her attempts to resolve the problem once she has truly identified it. Turning to murder, Magneto, and ultimately Apocalypse don't fit Moira until she's learned just how truly dark the truth of the matter is. And each, increasingly radical, strategy she employs is tailored strictly to resolving the problem that she identifies during the events of life 6. Her taking those paths before she learns the true underpinnings of the problem, when she has exclusively pursued Xavier's course prior to her realization, doesn't fit.
As to your second point, that it doesn't make sense that she'd just abandon old allies, I think that speaks to the person Moira has become. She appears coldly manipulative, able to turn on anybody, use anybody to achieve her ends. She appears capable of still caring for people, of empathizing with them. But she can discard any attachment, abandon any personal loyalty. Her goal is what matters. She has been radicalized, as the story explicitly tells us. Her mission is what matters to her, people are tools to accomplish it or obstacles that must be overcome.
It does give her a rather more sinister aura, if one chooses to see her in that light. And makes Xavier and Magneto following her feel almost alarming at times. All of which I think is rather the point. It feels like we're SUPPOSED to be just a little bit hesitant with these new developments. Yes, mutants get a big win in House of X. But Powers of X makes it seem like everything is hanging by a few very delicate threads that not everyone involved can truly trace to their origin points. And that Moira herself may almost certainly be an unreliable narrator. I feel like we, the audience, have been placed in the role of Xavier and Magneto. We've seen exactly as much as Moira (or Hickman, if we want to be meta) wants us to, and through the lens that she has chosen to view it. And left to wonder just how much we perhaps haven't seen, or how much context we may be missing. But we must move forward, either in suspicion or faith. The drama moving forward will be how the players play out Moira's game, and how Moira herself perhaps reacts to the movements they make.