: But from what I remember, the Warden implies that it was "prophecy"
: or some such, and Halo 4's Librarian more or less said that it was
: "the plan all along". Elevating the MC to pretty much a Jesus
: figure, and Cortana as the next programmed step in destiny... It's pretty
: dumb either way, especially when you hold it in contrast to the story
: being told in the Bungie era where Mendicant Bias was pretty much the
: pinnacle of their AI, and the downfall of the Forerunners...

The Librarian's plan is what she called it—an eventuality. Humans would eventually come up with power armor and AI assistants and all the tech stuff they once had, and the Librarian wanted them to inherit all the Forerunner's gadgets (she never called Master Chief into existence). But she didn't want them to inherit the Mantle, which she held as one of the reasons the entire galaxy fell to the Flood (this goes all the way back to Halo 3).

The Forerunners held that the Mantle is basically a responsibility awarded to the top dogs of the universe (them) and they used it as justification to suppress anyone else from reaching their level of power. That's what the Didact is going on about, although he couches it in your usual "I'm doing this for your own benefit." Cortana and the Warden are saying that AIs are the inheritors of that legacy, not frail meatbag humans. The whole painting their assumption of the Mantle as "the real plan" is just wrapping their regime up in some trappings of legitimacy. "Believe me, if the Forerunners were here, they'd totally agree with us on this one. So be quiet or I'll send my space bird to nuke your technology."