I never liked Halo 2, the campaign gameplay was just so inconsistent for me. But I replayed it after some years to prepare for Infinite and I realized how CLOSE the Covenant came to annihilate Humanity if Prophet of Regret kept his chill.
Seeing how Truth led a huge Covenant fleet, bigger than the one on Reach, to Delta Halo… he could have brought that fleet and just mass swarmed Earth, then the Ark, and just ended it from there.
I also realized that even though Miranda got the key from the library, Amber Clad was taken by the flood. How did they plan to escape in the end with her and Johnson.
Unless I’m missing something from the comics or whatnot, if the prophets had some backbone, UNSC could have been fried…