You asked if anyone ever just free ranged the chickens. We did, almost. I gave the chicks feed until they could manage on their own. Then, fed them whole corn, whole oats, whole wheat, (and sunflower seeds in the winter). They mostly foraged in the summer. We used to have sheep so they could scratch in the manure to look for larvae. In the winter they mostly had the seeds.
Now, with chicks, I don't feed them commercial feed to start. I feed a mix of corn meal, quinoa, chia, a little fennel. When they go outside they also have bugs and vegetation. I add bits of meat when the insects disappear. I don't believe they do as well without meat of some kind (insects or hamburger/pork burger).