I don't understand the notion of everything that isn't layer crumble being a "treat."
Fruits and veggies are loaded with vitamins and minerals.
The exact things that are "treats" for birds, doctors can't get us to eat enough of.
Then we throw them a crumble and say, "that's all they need."
Meanwhile, anyone with half a brain knows that you can't get everything you need just swallowing vitamins.
I'm not saying you should be feeding low-nutrient stuff like scratch all the time, but my god, I was covered up in eggs last year and the chickens got everything from the garden that I didn't use and even then they got the leftovers.
Yes, I feed an 18% all-flock, so it's not hurting protein as much as those laying lower protein mixes, but good lord. A head of cabbage or a tomato isn't cotton candy.