Yes, you are correct. Chickens lived for centuries without the "help" of universities and commercial feed companies. No doubt about it. However, in our incredibly complex and competitive society today, we must make the best use of our resources, time and labor.
I am privileged to have observed the chicken raising methods that my grandmother (may she forever rest in peace) employed. She raised almost all her birds herself, and didn't purchase them from hatcheries. She didn't use commercial feeds either, because they were not as readily available as today. I can tell you that her birds were healthy and produced well for her at that time. However, in this highly competitive day and age, her methods would put her out of business quickly.
She utilized the ultimate "free range" system of raising her chicks. She would allow them to free range about the farm till fall. They were basically "on their own" as far as finding feed. They would glean feed from the cow pies that had some undigested kernels that passed through the dairy cows. They would get a bit of feed from the hog pen (pigs are notoriously wasteful), and also they would pick up a lot of grain from spills around the farm. Of course, they ate a LOT of bugs and worms from wherever they found them.
In the fall, she would round up all these young chickens and pen them up to fatten the ones that she planned to butcher. The young leghorn cockerels and many of the white rocks that she planned to butcher would be placed in a pen and fed buttermilk, ground corn and oats, and whatever kitchen scraps she had from day to day.
Her future laying hens were penned in the chicken house, and prepared to start producing eggs. These eggs were traded in town for groceries and occasionally some cash for the household. These birds were fed basically the same as the dairy cows (corn and oats). The protein was not very well balanced, and these birds were forced to eat a lot of extra feed in order to obtain the required amino acids that are necessary to produce well. Since grain was very cheap in those days, it worked out financially for her, but with today's high grain prices, it would be prohibitively expensive.
Now, this may sound like an idyllic lifestyle for the chickens, but bear in mind that there were many that didn't live till fall. My younger cousin and I were in charge of predator control. We routinely shot hawks and owls (it was perfectly legal at that time), trapped rats and mice, and killed every other predator that we could. Still, many birds were killed each summer by various predators, including the voracious pigs.
In the winter, grandmother would baby her hens a lot. They received all the ground corn and oats they could eat, and sometimes she would place a bale of green, leafy alfalfa in the coop. Again, at today's prices, this would be very expensive, because the birds were not getting the correct amount of amino acids. Therefore they had to eat more feed in order to get the amount of amino acids that are required. The rest of the feed was essentially wasted.
What I'm trying to convey to you is that well balanced, scientifically blended feed is cheaper in the long run than trying to blend feed yourself. Granted, there is a certain amount of satisfaction in knowing exactly what ingredients are going into your feed, but most of us are not nutritionists, and could easily short change our birds on a necessary mineral or vitamin. This would likely make our birds have to eat more total feed in order to supply themselves with whatever is missing. Again, at today's grain prices, it would add up quickly.
Since many of us are hobbyist poultry magnates and have low numbers of chickens, price is not a big issue, and whatever makes you happy is fine. However, with the economic downturn, saving a $ here and there is important to some, and feeding the best-balanced feed makes the most sense in the long run.
Just my opinion!