You should really lay off a guy who JUST got trade to us and has played 3 games. It takes awhile for someone to go from being the #1 option on a team and the face of a franchise to settling in as a role player. Wallace is very very good and he has played fairly well but has picked up some stupid fouls and made some stupid mistakes because he isn't used to playing with our guys. If he still isn't fitting in after another two weeks i'll look a blind eye as you get on him.
In my opinion it is the constant switching on screens that is causing the defensive problems. When you switch on screens (that involve LMA or Camby), your defense is immediately at a disadvantage. First, when you switch, LMA or Camby is forced to guard the quicker guard on the perimeter. Most of the time the guard is going to blow by them straight to the basket (i.e. Kyle Lowry on Tuesday night). Second, when LMA or Camby is forced to defend the guard on a switch, that takes away length and shot blocking away from the basket leaving the middle vulnerable. Third, there are two immediate mismatches, LMA or Camby on the quicker guard and Andre Miller on a bigger PF or C. This leaves our defense in constant scramble mode and on its heels. The elite teams like the Celtics, Lakers, Spurs do not switch on screens. They either have the big man hedge aggressively or they just have to fight through the screen.