I grew up on one of those farms. With good quality forage, the chickens can do quite well. By good forage I mean grass and weeds, grass seeds and weed seeds, flying/hopping bugs to catch and creepy crawlies they can scratch out of leaf piles or whatever. The only time we fed them anything was in the winter, and that was home grown field corn, shelled but not crushed or ground. They did have access to the hay barn, but most did not spend much time in there, even in winter. There was cow and horse manure for them to explore. We did not often have the ground frozen all day and did not have a lot of days snow covered the ground.
They did not grow as fast or lay as well as chickens fed a complete commercial mix designed to maximize efficiency. I'll argue which is more efficient though, a flock where 50% of the hens are laying and you are paying nothing for feed versus a flock where all the hens are laying practically every day but you buy most of their food. They did not grow as fast or as big as chickens fed a high protein diet, but we paid a whole lot less for the feed and one would still make a meal.
Not all of us live in conditions where they have top quality forage. I clearly notice that my broody raised chickens forage a lot better than my brooder raised chickens today. Back then, they were practically all broody raised chickens. Mine today are descendents from current hatchery stock, not some throwback genetics. I don't manage them the same way my parents did, but I really believe the ones I have today could do as well foraging if they had to after seeing my broody raised chicks. They may have a learning curve, but they could manage.