Lol we're actually debating this
, I don't mind though, I love the movie.
Harvey coined it 100% but the phrase that he coined was mostly foreshadowing, however inuniverse it doesn't mean much as inuniverse he was mostly referring to the corrupt ways at which the city was run aka bent cops like ramirez pretending to be good guys. It was nothing more then just a hunch.
The line by batman was iconic as not only is it revered more due to the end of the movie being one of the greatest endings of all time, but inuniverse it was a representation of what actually happened.
Harvey became the villian but he would be remembered as a hero as no one would know the truth(Before Bane that is), and batman would become the villian.
Aka harbey: the hero who died
Batman: the hero who became the villian.
Batsmen's line delivery makes more sense. Harvey's line is just foreshadowing to the audience that's all.