“To which I would add that hunting the domesticable animals into oblivion seriously retarded agro-urban development and condemned many tribes to permanent seasonal nomadism.”
Yes. But bear in mind that New World beasts and “native” Americans were not coeval. Humans came over here fully prepared to hunt everything to death. The animals had not enough time to evolve defenses. Back in the Old World, there was time to breed (though not deliberately, of course) animals to our liking over the course of millenia.
In the late Pleistocene, this continent wasn't exactly an Edenic landscape, particularly the upper Midwest. Humans exerted a profound influence, particularly after introducing the Asian bison.
The animals had not enough time to evolve defenses.
You underestimate the humans. Canis dyerus was no puppy. Neither were mammoths or the bison that was here. It is a simple fact that the humans that came here were simply voracious and extremely capable hunters not interested in developing domestic livestock, much less a settled lifestyle.
There were stock here that were suitable for development. Shrub oxen, a small camel, and a small horse, but they were good to eat and were soon gone. Certainly some of the sloths were good potential meat animals.
The animals had not enough time to evolve defenses.
LOL, grizzlies did OK. We disagree. IMO what happened was because of the cultural attributes of those who first arrived. In my opinion, entire continents take the shape pursuant to the values of the people in charge. We are that influential.
I am simply unwilling to look at humans in a strictly biological fashion. There is no other species on earth that even remotely approaches such a profound effect on every level of the food pyramid as humans, for good or ill. Evolutionary models are simply not that accurate beyond closed systems, and for the most part, do not include people as an integral component. It is either an egregious mistake or wishful thinking on the part of a misanthropic few.
There is also the matter of the discover of Native American / Mayan / Inca toys with wheels, but no one realized it had any value on the roads they did build.