I don't think it's "gotta be", but he is an all time great, and I don't throw those terms around.
Sanchez is the most intriguing as he had such a dominant run, and then died before his prime. I think he was the most talented of the top tier Mexican fighters, we just never got to see what he could be.
FYI, interesting overview:
Also interested to get thoughts on what the definition is of "Mexican" fighter. Do you mean place of birth, place of residence, or ancestry? As an example, Oscar marketed himself as Mexican-American for his whole career, but was born in the U.S.. And there are a number of fighters, born in other countries, who move to America for different reasons. If a fighter is born in Kazakhstan, but his family moved to the U.S when he's 5, is he a Kaz fighter? If a fighter comes from Cuba, when he's 20, is he a Cuban fighter? What about fighters who pursue different citizenship for Olympic purposes? Just thinking out loud. This is interesting. Thanks for your patience.