It seems to me that the authors were just assuming that this specialized force would be 1) ready when needed for a future conflict, 2) available at the time and 3) in the right area with its resources.

I sincerely doubt a specialized counterinsurgency unit could meet any of those criteria. Had such a unit existed in 2003, it's personnel, equipment and training resources would probably have been raided to make up for shortages in the line units getting ready for OIF. It also would already have deployed everyone else to Afghanistan. Finally, the process of readying and moving the unit to Iraq would have taken quite a long time.

Even when such a unit is up and running, there's no guarantee that a high intensity force would be needed to deal with a blowup like Fallujah, Ramadi or Najaf. And all three of those happened at about the same time! This hyped up advisory corps would have been storming Fallujah by itself when their Iraqi recruits folded. In Ramadi, they'd have been overrun.

General purpose forces will never be ideal for any mission. But it seems to me (as a civilian) that in war doing something now is more important than doing it perfectly.