You’re over thinking this. Since you’ve successfully raised chickens in the past trust your instincts. Chickens today are no different now than when you raised them.
Commercial feeds, whether National Brands (e.g., Purina or Nutrena) or Regional Brands, are specifically formulated to meet the dietery requirements of poultry at specific life stages (i.e., starter, grower, layer, etc.). These feeds contain all of the nutrients, vitamins, minerals and probiotics at the daily dietery levels needed for a healthy flock. The majority of people (me included) do not have sufficient knowledge of the specific daily dietery needs of chickens so commercial feeds take care of that for us and our chickens. Chickens whose dietery needs are not properly met are more susceptible to disease or infection (e.g., necrotic enteritis) caused, in part, by an imbalance of their intestinal flora thus allowing bad bacteria to flourish. So, unless you have a working knowledge of how to properly mix a nutrient complete feed, I would suggest you feed commercial. If you do have such knowledge then go for it.
I’m also of the opinion that it will be more expensive per pound to purchase all of the ingredients needed to make your own complete feed. Scratch grains, mealworms, etc. are good for treats in moderation (10% or less of daily diet) but are not a complete feed.