I don't know, because I am not in the training camp with them.
On paper, a lineup of:
Paul
Wade
Bowen
Brand
Bosh
... could be a very good defensive team.
Anthony and Arenas are the worst defenders on this team. Neither Paul nor Hinrich are huge defensive specialists, but they are good enough to stay in front of people in most cases.
Stoudemire and Howard are not bad, and Miller could be a better defender with internaltional rules than he is in the NBA. Defensively Lebron James in an unknown quan y... he could potentially be a GREAT defender, but he has to put his mind into it... he very often has lapses, cheating off his man, not runninng, etc. If he starts missing defensive assignments, I would bench his ass and put Bowen instead.
In any case, defense is more effort than X's and O's. Rotate, help, communicate, cover. The coach has to find the right group of guys that communicate and help each other. He has 25 more days to find out.