Are we talking about 1500CE, when the Christians began obliterating all New World civilizations and advanced Neolithic communities that were precursive to civilization?
No, the specified time frame was during the peak of the Pueblo civilization - that's around 1000 AD. London only had a few thousand inhabitants at that time. The civilization in question had long since collapsed by the time any Europeans showed up.
Neolithic agriculture was a full-time job, and full time in those days meant 100-hour work weeks except in winter, when they repaired and replaced their tools. It was difficult for a family to produce significantly more food than they needed for themselves. This is why more than 95% of the human race were doomed to be farmers until the Industrial Revolution improved their productivity in the late 19th century.
But you do agree that there were "cities" and "civilizations" prior to the industrial revolution, yes? And so the fact that most all Pueblo labor went into food production does not disqualify them from building cities any more than it disqualified any pre-industrial European settlement from "city" status?
If you're saying that it's easier to produce larger surplusses with progressively better technology, well, I can't disagree with that as a general proposition. But that's far short of an argument that the Pueblo peoples didn't manage to produce sufficient quantities of food in a sufficiently centralized fashion to end up building cities.
But let's not forget that the North Americans had three deal-breaker disadvantages compared to their Neolithic counterparts in Asia and Africa.
Again, you're speaking in generalities here. The fact that Four Corners dwellers had certain disadvantages is not actually a positive argument that they didn't have cities.
Also, they had domesticated turkeys, so it's not clear to me that the protein disadvantage of corn was a huge deal.
The only definition of "city" I've seen in this thread is "settlement big enough to have permanent buildings and for inhabitants not to be acquainted with everyone who lives there (requiring systems of law and order)." I contend that places like Chaco Canyon and Mesa Verde met that definition, whatever their handicaps regarding agriculture might have been. And I assert that such cities were centers of trade and governance for much wider surrounding areas. They were the center of a large turqoise processing and trading industry. They were quarrying blocks and felling timber from far-flung places, and then transporting it to the central cities, and using it to build structures that remained the largest in North America (which included the Aztecs, note) until well after the American Revolution. And they had a system of highways extending hundreds of miles to boot.