Understand that chicken have been some of the most micro-studied of all animals for nutrition. That is because they are such a large part of our food system and (when factory farmed) are 100% controlled. You can't even say that about cows that eat primarily grass, but also a lot of semi-random greens for the majority of their life. Only later in life are many cows grain fed to fatten them up for slaughter.
Now, think about exactly why they are studying chicken nutrition so closely. What are their goals? They want low cost and high volume production, both for eggs and meat. All of the chicken nutrition guidelines are based on these factory farming priorities.
What aren't they concerned about in these studies? Long-term health of the birds, humane growing practices and optimized nutrition from the resulting eggs/meat. Many backyard chicken owners put higher priority on these aspects of chicken raising.
Unfortunately, we don't have nearly as much info on ideal nutrition for these additional priorities, mostly just tons of anecdotal experience. Protein levels are simply the most visible nutrient that we try to optimize.
As others have mentioned, I also follow the all-flock + calcium feed method to try to improve nutrition beyond the factory farm minimums.
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Humans can can and do also survive on less-than ideal nutrition. They will just have stunted growth, intelligence/psychological issues, poor health, reproductive problems and/or shorter lifespan. The US RDAs (recommended daily allowance) are exactly the same as the chicken nutrient recommendations: minimum, not optimal.
One concrete example: the US RDA is 150 micrograms of iodine/day. Why that level? Too many American men were rejected from military service in WW1 due to goiter (inflamation of the thyroid) from low iodine. They established the 150 microgram minimum to prevent goiter, not optimize health. Iodine is used in every cell of the human body and we would die without it.
Lower (RDA approved) iodine levels are heavily tied to thyroid insufficiency, breast cancer and many other health problems. I take 5,000 micrograms of iodine/day (33x the US RDA) due to all I've read on the subject. It is definitely possible to consume some nutrients to the point of toxicity, but excess iodine just gets peed out.
I wish we had better info for optimizing nutrition, but optimal health doesn't drive profits, so that isn't what's studied- for chickens or humans.