Yes, your observation about head hair in relation to body hair is correct. I agree that most (not all) guys with exceptionally dense head hair generally have less body hair. I am part Native American and have very thick head hair, very little chest and arm hair, and moderately hairy legs when younger. This dispersion is common among Native Americans, Mexicans, and Asians. Balding is rare among these groups. Perhaps it has something to do with the amount of DHT among these groups.
I honestly can't recall EVER seeing a bald Mexican/Latino. I have seen a handful of Mexicans and other Latinos with exceptional beards, and chest hair. Hairy legs and arms is a mixed bag. I see them both smooth and with lots of leg hair.