I don't really understand why scratch is considered so bad, if part of a wholesome, balanced diet. It's cracked corn, barley, Milo and wheat. Have you looked at a bag of chicken feed? It's grain by-products, wheat byproducts, corn, soy, lots of vitamins and such. I agree that they need the added soy and probably some extra vitamins but if they are on fresh pasture, greens and bugs, they are getting a pretty good mix of b-vitamins, vitamin A, vitamin C and probably a decent amount of protein from fresh young grades, grass seeds and bugs. Those bugs are surprisingly nutritious.
I've learned, from seeing my dogs and horses health improve after taking them off their " complete and balanced rations" and replacing it with more species specific diets not made by big companies like Purina that we can actually feed our animals real foods and do a pretty decent job of balancing rations. It's when they eat the same thing from the same over processed bag day in and day out for years that dietary deficiencies become obvious.
Of course, if your birds are in an enclosed coop and you don't have access to fresh fruits, veggies, grasses and bugs, things become more complicated. Winter in most parts of the country are also more complicated. But, don't be so trusting of big feed companies telling you that they are giving you magic formulas in every bag. They aren't that magic.