{ but many many Mexicans are actually natives}
This is actually true because California and some other states were part of Mexico so many Mexicans would naturally have roots in these regions.
If 90% of native Mexicans were wiped out in the first century, that would mean those roots come from immigrants. Immigrants cannot be native to a land by definition.
If by native you mean from Spain, then yes, many Mexicans are natives. But real natives in that area spoke Arawakan, Aymaran, Cariban, Chibchan, Jê, Pano-Tacanan, Quechuan, Tupian, Tucanoan and Yanomaman. (thx to AI for research)
How far back will Trump take his no citizenship birthright? His ancestors immigrated to America. :/