I said THRIVE. Not live. There is a very significant difference. I actually read a lot of the thirds (and developing world) research on poultry nutrition to see what other ingredients are out there, to get ideas for things to try out.
But since you bring up the third world, I'll offer an illustration which may help you distinguish betyween my use of live and thrive.
The people of North Korea and South Korea are genetically, essentially one people. They've only been divided politically in the modern era. Obviously, man has lived there for thousands of years. LIVED. To the people of the still third world North Korea, men their look normal, natural, more or less as they have for thousands, or perhaps tens of thousands of years - living a lifestyle not much changed from their ancient forebearers.
When a North Korean male crosses the border and is compared with his South Korean counterpart, benefiting from greatly improvced diet, its obvious that the South Korean man is, comparatively, THRIVE-ing. He's pounds heavier, inches taller, has a generally more robust immune system - even before accounting for improvements in modern medicine.
Now that comparison becomes increasingly less far as the South Korean populace increasingly intermingles with more diverse genetic populations - but the studies and observations first noting the significant visual differences in size, weight, and general health trace back to the 70s and 80s.
But what does it mean to thrive in specific relation to chickens? Humans living hand-to-mouth may be having a less-than-happy life depending on the circumstances, culture, and wishes and personality of the individuals. If we take the human analogy to the next step, fat coop chickens would be the equivalent of humans in a razor wire prison being fed nice food but unable to leave. Is that thriving? Supposed calamity hits the South Koreans so that their nice food and healthcare vanishes. Wouldn’t then the rugged North Koreans be better positioned to survive the collapse? I don’t think a human analogy works here, but to the extent we’re going to use it I would think the poor North Koreans in the analogy are a tougher people than the rich South Koreans.
I would think that as far as chickens are concerned, being healthy through their prime years and reproducing at a rate faster than predators and disease can take them is thriving. If we define “thriving” to be equivalent of relatively rich human living conditions in the first world, then no wild animal really thrives in a state of nature.