The issue to some degree is that Kobe, Artest, Gasol throw a monkey-wrench into the equation in this Nash AND/OR Dwight discussion.
Let me explain.. Back in Suns days, Nash had to feed one guy in Amare in the paint while the other sharpshooters just stood around the perimeter. Kobe/Artest are no sharpshooters, but you know they are a big part of this team. Nash has to give the rock to Kobe for long stretches so you don't quite get to see Nash average 12-13-14 assists per game anymore because he is not in the position to do it anymore. Gasol also got in the way of Dwight for long periods on the court - look at Dwight putting up great stats with Gasol out of the lineup.
If you had just Nash and just Dwight with 2 other role-player sharpshooters on the perimeter in D'antoni's system, Nash would STILL average 13-14 assists per game and Dwight would put up better stats than his Magic days with a star PG running the system as opposed to a jameer nelson. I think it would work out perfectly fine with Nash AND Dwight. Of course, this team wouldn't be a contender for championship without Kobe, just a great regular season team.
As for Phil vs D'antoni issue.. I think DKLaker/takai/dd24 are right. Just one point though - I don't think Phil would ever coach this team if there was no Kobe and just Nash/Dwight/bunch of role-players. It just wouldn't happen so forget about stats or w/e. Phil wouldn't accept it, he cares only about championships.