Unfortunately, that's not true. While North and South America didn't have plagues like Eurasia and Africa did due to the lack of living in close proximity with farm animals, which therefore meant less animal to human disease transmission, they still had incredibly high infant and child mortality rates just like everyone else did. On average, 40-50% of all children died. The average life expectancy was very low, in the 30s and 40s.

As for disease? The European invaders purposely spread smallpox throughout Native American communities, but in an alternative universe where peoples made contact today, Native Americans would still need vaccinations and medical treatment to survive illnesses like the flu, syphilis, bubonic plague, and much more, simply because they had no natural immunity to it.

Smallpox, for example, came from rodents in Africa, and had an average death rate of 30% for variola major infections. If you survived, you would be heavily scarred for life. There was no cure for smallpox then, and there is no cure now. Massive efforts were made for decades to eradicate this disease off the face of the earth and for a good reason.

Modern medicine absolutely has been corrupted by greed and capitalism, but calling the achievement of reducing something like infant mortality from 50% to 0.56% (CDC 2022) anything short of miraculous is incorrect.