: tl;dr - Cortana's actions are quite possibly the result of her being
: manipulated by Precursors as part of an effort to test humanity's
: worthiness of assuming The Mantle of Responsibility for All Life. The
: original Cortana wouldn't behave like this, let alone speak in the manner
: that she spoke at the end of the game, and therefore she is presumably
: being puppeteered or manipulated by something far greater.

Consider the Warden's caustic attitude regarding who Cortana is (has become), how John will have to destroy her (or otherwise oppose her)....makes sense within a contentious Forerunner-Precursor relationship, and contemptuous Forerunner opinion of humanity's worthiness.

He talks like a spurned ex-lover or something, with John as the new flame. I found his (it's?) bitterness and pettiness notable.

Further, how and why would all Foreunner constructs immediately follow the ascended Cortana, unless she had some sort of real advantage over them? Cortana was potent and powerful, but she was also almost rampant and would have found Forerunner constructs a challenge in any case.

The Warden did not strike me as a happy vassal.