I believe you are very much mistaken unless your definition of "geographically stunted" and "has always" is different than what is generally accepted.
The facts show clearly that prior to 1492, Central and South America were where the larger, more organized, more sedentary, more productive civilizations were. That's why the Incas, Mayas, Olmecs, Aztecs, were all NOT in North America. So any theory of "geographical stunting" would need to explain what changed in the geography after 1492.
> Without the cooperation of the natives, Europeans could get nowhere.
I'm surprised that anyone would believe this "cooperation" of the natives. I have a simpler explanation. "Natives" did not cooperate willingly. Instead, through our vastly superior military technology, we imposed "cooperation" on the natives in Central and South America, while in the North, we imposed something completely different as already explained above. In the Central and South American region, we setup political and military structures to preserve ourselves at the top and keep the entirety of the other population at the bottom and also to prevent their escape. That was the defined purpose of the encomiendas. We wanted to do the same in the North but could not. North America escaped this fate precisely because the native population was far too sparse to enable viable encomiendas. So our corporations had to find alternate ways to gain profit, and that turned out to be, by enabling and giving rights to the settlers/colonialists. That difference is effectively the primary cause of what has given rise to the vastly different fates between the 2 regions.