This discussion gets distorted. In 2003-04, the Suns held their opponents to 44.6% shooting. In 2004-05 the Suns opponents shot 44.5%,
After that, the Suns opponent's shot much better
2005-06 45.4%
2006-07 45.7%
2007-08 45.6%
There is about 1% difference between top 5 and middle pack (Lakers were 44.5% last season and ranked 6th).
Some of problem even these stats have can be understood in terms of D'Antoni's reluctance to foul guys making layups. The impact of this on the stats may be bigger than most people suspect. Take last night's Cetlics / Pistons game.
In game 3, the Celtics shot 32 of 69 (46.4%) and 25 of 30 from the line.
In game 4, the celtics shot 21 of 66 (31.8%), but hit 31 of 39 free throws.
The extremely physical defensive style the Pistons used in game 4 led to a lot more fouls, but seriously disrupped the Celtics offense. Sheed and Rip both finished with 5 fouls while Prince, McDyess, and Hunter each had 4.
Being willing to foul a lot is something D'Antoni refused to do. For one thing, he lacked the depth. He hated losing his strong offensvie players to foul trouble. His style of wearing out opponent's slower players was build on keeping the game moving and not letting them rest while standing waiting for foul shots.
Obviously there is more to it than that. Nash is too small to be a good defender and Stoudemire too inconsistent. More emphasis on defense might have helped, but does not explain why the Suns were better on defense in 2003-04 and 2004-05 than later.
My suspicion is that the Spurs style was being copied by opponents in that they would post up. Marion required double team help and Amare was getting physically overwhelmed into fouling.
So while D'Antoni did not stress defense enough, I'm not sure he didn't care. It's just that he was not willing to sacrifice other sfuff to get improvements. But in the playoffs, that didn't get it done.