I think having Salmons out has a roundabout effect on our defense, since Garcia can't be fully depended upon for a solid 25 minutes at backup SF (because you never know which Garcia you're going to get), and this in turn puts pressure on the front line, because you don't get those 10 minutes a game with Ron at power forward. Instead we've seen more Corliss at center, and that tells you all you need to know. Salmons might also have been more attentive than Garcia and wouldn't have let Barry bomb open threes the whole second quarter. But he is by no means THE reason the defense hasn't been good.
But mostly I think having him out has really hampered the offense -- he's the only guy on the team who has a calming effect on the offense, and the Kings have really missed the 25 minutes when he's in the game. When he brings the ball up the floor good things seem to happen offensively because he's good at spreading the ball, getting it down low, and occasionally looking for his own shot.