I see what you're saying, but Neal and Bonner are really the only two that are comparable. The other guys have flaws, but none are on Blair's level. But take Neal. He might be horrible on defense like Blair, but it's slightly more forgiving to have a bad perimeter defender than front court defender. With a bad back court defender, there's at least more distance to the basket that allows for more time for other players to help off their man, or the front court guys to protect the rim. But when Blair blows his defensive assignment, it's a layup for the other team. Neal's also shown he can hit big shots in the playoffs, which is a very valuable trait to have. With Bonner, the spacing he provides makes him very useful in the Spurs offensive system. We all have our problems with Bonner, but even though he's a pretty limited player, he's a much smarter player than Blair, rarely makes boneheaded mistakes, even if his limit skill level keeps him from being very effective on the court.
So I'd disagree that for any of our other bench guys, "the negatives outweigh the positives." I think the only player you can say that about on this team is Blair.