Danny's biggest mistake was dissing Tony Allen so hard that he took less money to go to Memphis.
Allen is a STEAL at his current salary. If Tony Allen stays, then we don't waste money on Marquis Daniels, Peaches, and string of other TERRIBLE swing men behind PP.
Plus -- if Marquis Daniels isn't around, then he doesn't get hurt, and Danny doesn't panic trade Perkins for Jeff Green.
He either uses his leverage to move Perkins for Harden (which was the player he initially targeted), or we win the title that year with the team as constructed.
Most of Danny's worst moves are the result of him treating players like their cards in a card game instead of people. He drove Tony Allen out of town. He dragged Ray Allen thru the mud so long he took less money to go to Miami. He murdered the whole ethos of the team with the Perk trade. (And while that trade looks good now, we essentially traded a title shot (potentially 2) to be a slightly better mid-tier team in 2013/2014. That's not value in my mind.)
He's an excellent draft evaluator, but his free agent signings are borderline criminal. Besides resigning his own players, who's the best FA post-2008? Stiemsma?
His big trades are good. His little trades ... not so much.