Maggette would improve as much defensively as POB did. His defensive deficiencies would be masqueraded, but they wouldn't disappear - and they'd bring the overall defensive quality of the team down.
I have no doubts about Randolph's massive upside - excellent athleticism, good rebounder, natural instincts. However, I have serious doubts about his ability to fulfil it. I don't know if the Warriors are really shopping him, but generally Nelson doesn't make many mistakes when it comes to evaluate players.
I have no doubts about Maggette's ability to fill stat lines in a consistent basis. However, I have serious doubts that he actually delivers wins while doing so - especially for a team like the Celtics. He's too much of a ball stopper, too self-absorbed and selfish. He takes his teammates out of the game. Do you really want Maggette as your go to guy whenever he's on the floor during the playoffs, when Pierce, Ray, Garnett and Rondo will all be playing close to 40 minutes per game? Because that's the only way Maggette knows how to play. One other thing I have no doubts about: Maggette is severely overpaid for what he produces.
None of the teams is doing this deal.