"But I wonder aloud, before I read it, wouldn't this imply that the military should have gone into Iraq with twice as much as it did? None of this lean and mean business, but more of a Powell doctrine? "

I couldn't find the numbers but at time of Gulf war I, the US miltary had more soldiers. In Gulf I we deployed around 1/2 million troops for period of war which lasted less than 2 months. We might be able to surge 1/2 million troops today for less than 1 year, but things would start break if we tried doing this for 3 years. Troops are stretched now, and we have 138,000 soldiers in Iraq. And putting 300-500 thousand troops in Iraq wouldn't really be Powell's doctrine- other than putting as much in there that is possible. It wouldn't give overwhelming forces in same sense of Gulf war I. Saddam army was extended into Kuwait, Kuwait is relatively small area. Iraq the entire country could swallow 1/2 million troops, and million troops would still not achieve this overwhelming presence. Then you have to consider logistic. Remember the problems with getting body armor and armored Hum Vees- double the force and this problem is AT LEAST double the delay to get all soldier fully equiped.
Finally you get the costs of doing this. At moment I think the total cost is around 250 billion. Double the troops and it's double the cost, so it would be at 500 billion. So if you go in there with twice or triple the number of troops, you will increase the costs, soldier will in general be less equipped and less trained, you will have even more shortage in number people who can speak arabic for translation purposes. And you still will have a similar situation as you have now, of most Iraqis not ever seeing a US soldier [not a big presence]. And finally you would get more US soldier dying as a running total. Now, you could flood small areas with high troop presence- if you put 200,000 in Baghdag that would probably be enough to project a significant presence that might keep order/quell riots/surge in violence. But they also potential targets such as to be mortared hit and run and they are going to interferring with Iraqis going about their business. I think it's debatable whether this would give good results- but certainly would cost more in terms dollars and soldier lives. And of course this wouldn't have done anything to stop the looting in the beginning- because you simply could not get enough soldiers in there in a short enough period of time.
Though you could went to Baghdag slower, and deployed more troops to hold the cities along the the route up there and by time you got to Baghdag the looting could have been over.