False.
Facts contradict your uninformed statement.
It's not about theories or anthropologist's opinions. It's about facts.
The census of the population of Mexico and Brazil is the source for the CIA Fact Books.
I lived in Texas circa 1970's. I've had some opportunity to observe mistaken identities. I had a hard time telling them apart. How does a modern census describe the population?
This is all not to mention Argentina, Chile, Bolivia, Peru Columbia and Venezuela. South America has a lot of the same kind of people for Mexico to be filled up with. Some even have customs identical to the Mexicans. All you have to do is look at the pictures of the people indiginous to the area.
You don't need CIA Factbooks. You just need your eyes.