GP was not talking about herbal remedies. Many modern medicines are derived from or inspired by plants.
https://www.thoughtco.com/drugs-and-medicine-made-from-plant...
https://www.thoughtco.com/drugs-and-medicine-made-from-plant...
And if they did it then there's absolutely no reason to think that modern pharma can't produce the same knowledge. And the whole assumption that there is a body of invaluable knowledge somewhere, held by indigenous people but somehow unavailable to modern science is very strange.