I don't mean to be rude, but that's crazy talk.
Steve Nash is still a top 10 pg in the league, statistically the best shooter in the history of the league and because of his defense (which can easily be hidden at his position) he's not an upgrade over Nate Robinson off the bench?
I don't even know if this really warrants elaborating but quite simply:
The difference between Steve Nash and Nate Robinson offensively is significantly greater than what Nate Robinson brings defensively. I mean, not even close.
Agree with your premise. However, the trade scenario takes Davis and Robinson off of the second unit. Substitute J O'Neal, who will contribute little or nothing until his contract year, and the deal looks a lot better this year....(Although I think Bradley is going to be a very good player with time and shouldn't be a throw-in in a deal). Davis knows the defense. So you're adding a great, great offensive player who plays no defense and subtracting a PF who knows the defense and defends well. Along with a guard who knows the defense and at least tries. Unless you think Harangody or some NBDLer is capable of playing as well as Davis in Davis' minutes, the starters, particularly Garnett, would be playing 40+. Garnett in particular because somebody has to be an anchor in a defense that's essentially short a man.
Nash's defense can easily be "hidden" during the regular season. His teams lose in the playoffs because defense matters in the playoffs.
The perfect team for Nash would have been the Sixers team Iverson went to the Finals with. Substitute Nash for Iverson on that team and they are a championship team. He'd be playing with the best defensive center of his era and for arguably the best coach of that era. Mutombo was one of the best defensive centers ever. A great defensive and rebounding power forward was among a perfect storm of role players. Nash would have made most of the shots Iverson missed. His defense would have been easily hidden by that group. A genius like Larry Brown would have been dangerous with a PG like Nash....As long as Mutombo was the anchor.