This is the same guy who drafted Alex Acker and Sammy Mejia...
... at the end of the second round.
Seriously, though, I know that missing on prospects is frustrating, but it happens all of the time; it becomes a problem when you don't have any good picks to offset your bad ones.
Dumars has drafted 28 players and has as many good picks as bad. You list seven "mistakes," but three of those guys don't seem to belong on the list. Maxiel is nothing more than a rotation player, but he was drafted as the 26th pick. The fact that he's playing at all distinguishes him from the few players drafted immediately in front of him and behind him. I don't care for Stuckey, but he's hardly a bust, given that he was selected at 15. Saying that Knight hasn't settled into the point guard position as a 19, 20, and 21 yrs. old is not equivalent to saying he was a bad pick. White was obviously a bust; I hated the Daye pick, even at the time; and the Darko pick... [obvious is obvious--but everyone would have done it--blah, blah, blah].
It's just as easy, in contrast, to find good draft picks: Okur (absolute steal at 37), Prince (great pick at 23), Amir Johnson (drafted at 56 and actually still in the league and producing for the Raptors), Afflalo (27, perhaps stupidly given away), Jerebko (plateaued after injury but drafted in the middle of the second round); Monroe and Drummond (perhaps no-brainers, but others passed on Drummond).
Joe Dumars has made enough questionable decisions over the last five years to get himself fired. I wouldn't mind him getting his walking papers. You're in the right to dislike him. I'm just not convinced that his drafting ranks all that highly on his list of sins.