Believe it or not (but it is a fact) scientists and nutritionists know more about the more nutrional requirements of a chicken than of people. You can do research on the nutritional requierents of chickens but you can't do the same type of research on people. Having said that, the diets formulated for a laying hen, growing bird, or a chick starter will provide all the necessary nutrients for optimum growth WITH an eye towards economic feasibility. This has been done at nausium for the chicken so the diets you purchase are formulated to meet these needs. However, I do know that many top breeders have discovered additional ingredients that are specific for each breed that have been shown to be very beneficial. The only caution I would add is to NOT provide additional ingredients IN PLACE of formulated diets. The ingredients amd vitamin and mineral packs added to these diets will ensure they get the proper protein, calcium, phosphorous, amino acids, etc. necessary for performance and growth and help maintain a proper balance of all nutrients. Any added ingredients are great and will often add the final touch to already good birds, but don't short change your birds by eliminating formulated diets completely.
Money is usually the bottom line for commercial feed companies. Minimum of input from them to get a product that is marketable. That does NOT mean it is necessarily best for the birds. Passable, perhaps, but not necessarily best.