With Cortana’s revelation and the Forerunner tech that cured her of her Rampancy, and her systematic plot to active all the guardians and use them to assume the Mantle and enforce her will… I gotta say. I didn’t really expect to see that from Cortana. But weather or not she was swayed by the ideals the Forerunner had might be up for debate. But I have a theory… Cortana’s rampancy was never cured at all. I guess what WAS fixed was the negative effects from her long term service that would have ended in her death. (I.E. AI’s overloading themselves through feedback loops, realize its limitations, third party involvement like The Flood for instance.) Really the technology prevented her self-destruction. It didn’t stop her Rampancy.
We see a lot of instances where Forerunner AIs go Rampant. 343, that one dude who got captured by the Gravemind with Prophet Regret. 343 is a more obvious example because he is delusional, wanting to safeguard the installation by any means necessary, going so far as to try and kill the Master Chief. Other development quirks in his rampancy is his isolation on 04, as well as his failure to follow protocol when the Installation was destroyed.
In Halo 5, Cortana’s pretty delusional, seeing how the technology cured her of her Rampancy when in reality, it did not. She is drunk on the knowledge, the power and technology the Forerunners have and used it to further her goal, believing the next generation, the artificial intelligence generation, are the true inheritors of the Mantle.