The problem with the 7 seconds or less systems is that you make defensive sacrifices to run the system. For instance, you have less people to crash the boards because you always have guys ready to run on the wing. In addition (as D'Antoni is proving in New York), the type of players needed to run this system are more geared toward offense not defense. There are very few players who are dominate on both ends of the court. So to build a team that can run 7 seconds and less and defend very good is a monumental task IMO.
It's all great to score offensive numbers like that. However, in the end, can you get enough stops to go all the way? I have seen no evidence of that in the D'Antoni era or post D'Antoni era. There have been other high powered offensive teams Mavs, Kings, Golden State, Suns etc...they all have two things in common. Crappy defense and no rings. So, we might have the best offense ever but still have nothing to show for it. I would trade the best offensive in the world for team that plays balanced on both ends of the floor in a heartbeat.
I kind of compare that to the old Run N Shoot NFL systems that everyone was running for a while. Teams went out and stocked up on offensive talent to run the system but had nothing on the other side of the ball. Those teams put up unreal offensive numbers but none of them could defend worth a lick and never went anywhere.