One estimate had Mexico with a population of 16 million in the year 1520 when the Spanish arrived, and a population of 2 million in 1620 a mere hundred years later. Yes, I bet it is true that most of those dead never even saw a Spaniard before they died.
Your population estimate cited for Mexico is similar to those used to portray the US as chockfull of Indians before evil whites came and eradicated them. In fact, their primitive cultures and technologies prevented them from ever sustaining large populations close together. Some historians maintain that the plains Indians weren’t even there when whites arrived, but rather are descended from tribes on the East Coast that were pushed westward.
Indians in Canada don’t gripe because rather than move them the Europeans could usually leave them where they were; they weren’t large populations and there was plenty of land.