To be fair, Krstic, Murphy, and Green are still learning the system, and the C's play a complex defensive system. Yes, these guys are not shot blockers, but once they learn the correct rotations, it is going to make a big difference on the interior defense.
Also, tonight, the perimeter defense was a much bigger problem than the interior. Yes, they were getting layups, but that is because Nash and Brooks were being allowed to get deep penetration which forced help, and led to the open shots.