The number was perhaps greater at one time or another. The population of Mexico in 1491 was perhaps the same size as that of France. As for the superiority of the “modern” civilization, please note that the average immigrant to Virginia lived about seven years in the colony. It took the English at least three generations to acclimitate their new environment. To do so, they had to utilize the technology that that aborgines had developed over time. For the longest time, they could not survive the winters without resupply from England.
There is no evidence of any permanent settlements i.e. cities in North America like that in central America under the Aztecs. Leftist historians dispense with the truth in order to support their twisted vision that the Indians of the Americas all lived in perfect harmony with nature until the evil Europeans came along. The truth was the opposite: the Indians of the Americas had segments of their populations who just as cruel, warlike, and rapacious as Europeans or other peoples of the world.
Look at the Mongols. American Indians are descendants of the Mongols who invaded Europe and southern Asia (not the other way around)slaughtering millions and leaving no cultural improvements in their wake...just death and misery. At least the Indians of the Americas contributed some wonderful vegetables to the world. But they also contributed tobacco which has killed multi-millions.
Again, the hard truth is that the Indians above the Rio Grande were small in number. Not more than a few million. If there were numbers substantially larger than that, unbiased historians would have published that fact. Every time I read stories purporting to show the populations above the Rio Grande around ten-twenty million, they're based on sheer speculation and not anything resembling hard data i.e. facts. The simple facts are: no large cities and settlements; no large Indian populations.