Chickens have never been so pampered in their history as they are today in American backyards

Historically, nobody has cared about the percentage of protein they ate, or whether their feed was organic. Chickens were recyclers, eating food waste that people threw at them, and whatever they could scavenge. And they survived. BUT. The important difference here is that their lifespans weren't long. Nobody expected them to live for 10-15 years and be healthy pets that didn't rack up vet bills. They just had to make it for a couple of years before being turned into soup. That's a pretty low bar. Chickens can survive for a couple of years on very low quality crap. The problems of improper diet need time to catch up to them - time they didn't have, so it didn't matter. Today, people raising chickens as pets or as a backyard hobby, want to squeeze ever more out of them, so a healthy diet is more important. So they watch the protein percentages and the nutrition labels. That's why it really depends on what your own chickens' purpose is. Are you going to cycle them every year or two when their laying slows down, and eat the retirees? Or are you looking to extend their lives so they can be family pets for a decade? This, plus the availability of feeds, will guide your decision as to what to feed them. If you live in a poor area and are struggling to provide clean water, I'd say focus on your family. The chickens will be fine on whatever you can manage, and when they stop being fine, eat them and get new ones.