Our layer feed has 17% and the Gamebird has 22% It also has all the other things that chickens would need with the calcium exception. It also costs more. You could feed it with just Oyster shell free choice on the side and be fine. I don't exclusively fee the crumbles because I find there is more waste with the crumbles as they seem to prefer to scratch their feed out of the feeder and eat it off the floor of the coop.We also bake and re-feed our egg shells to help with the calcium. We also give veggies and other scraps and they get several hours a day of free range time so they are eating seeds, grass, bugs - whatever. Most people don't realize that chickens are really an omnivore - they eat plant matter and "meat" in the form of bugs, frogs, mice, snakes, whatever they find. Tiny little dinosaurs with feathers! They do need their protein.
I started out feeding an all-flock feed that was higher protein and gave them oyster shell on the side. I then went to a custom mix of whole grains mixed with all-flock, catfish feed, and alfalfa pellets. (Oyster shell and grit on the side again.) They also had free range time and if they didn't I would always throw in the grass clippings from the lawn mower and bales of good quality hay to keep them occupied and the coops/runs smelling good. In the fall, they got lots of leaves. This allowed them to satisfy the need to scratch and catch any bugs, etc. that are in the organic matter. Best of all, free mulch. If my place had any rocks on it naturally I wouldn't have had to give grit, but the only rocks were those I bought and brought in.
Again, that is just my experience. I always had chicks and grow-outs and guineas, ducks, etc. so it was just easier to feed one feed that satisfied all the flocks without having to remember this one gets this or having to change.