Chickens really need animal proteins, so no matter how high a protein feed you get it's always just gonna have soy protein in it anyway.I never encountered feather picking,,, and think low protein may be a leading factor. I feed 18% Alflock.
Even when being feed a sufficient protein feed, some chickens may need more for a variety of reasons.
One of my theories, is a particular chicken produces more eggs than normally would with a standard ration. She then needs more protein.
One quick way to increase protein ,,,,, is to give the girls some (I did not say to overdo) cat food.
(cat food is higher protein %% than dog food)
Easily seen in my Avatar,,, that the girls like to raid the cat dishes when possible.
I don't think @SonoranChick hens are overcrowded. Seen that BEAUTIFUL PALACE her DH built.
I ALWAYS see increased egg production, feather condition, and overall health when I add animal protein to my birds diet. There is a Dumor chick grower crumble at TSC that lists animal byproducts in the ingredients and that's the 20%, in the 20lb bag only. But when I can what I usually do is get pond fish pellets. I think it's like 25lbs for $13 at TSC.
In the summer I make a wet feed out of regular feed, the pond fish pellets, scratch, and some alfalfa/bermuda pellets sold for horses. I add just enough water to cover it all, then let sit for at least 12 hours, longer is better because then it starts fermenting a little bit. It swells to another 1/3 the volume, and it makes everything more digestable, especially in the summer heat. They LOVE the stuff. I would rather get the turkey grower mash they make at the feed store down in Willcox as they add fish meal directly to their formula, but it's a 2 hour drive one way, so not really feasable.
Plucking can also be a sign of bordom.... just a thought. Maybe some saw horses, pallets, random beat up lawn furniture, variety of shady places and things to hop around on to make their area more interesting may help?