I'll cliff-notes it. Green was taken 30 picks after Daye. He got cut by a new administration and proceeded to put up strong numbers in the d-league. He caught on with the Spurs and didn't stick until Pop and Williams told him to focus. He was a starter by his third year, but he put up strong per-36 stats his whole career. Pretty much, Green is just a better version of the player he was when he won a national le with UNC. He just needed someone to stick with him.
Meanwhile, Daye was a mid-first-rounder who's been struggling to market his best skill. He got 12 times the number of minutes over his first two years than Green did. He put up decent rate stats, but he was a net negative for most of his career, ad opposed to Green, who was one of the most impactful on/off players on the team during his third year.
I like Daye, but he'll have to prove himself in an entirely different way than Green did. Danny was always a super role-player. Daye's justa guy with talent. The Spurs will have to mold Daye into rotation player, whereas they just had to fit Green in.