For thousands of years, before and after they were originally domesticated, chickens thrived on what they could forage. My father kept a flock that totally fed themselves on forage. The only time they got any feed was some corn when there was snow on the ground to interfere with their foraging. I don't know what your foraging looks like but if the feed is available and they are not eating much of it they don't need it.
If you keep them so closely confined that they cannot forage and you micromanage everything they eat then treats should be kept to 10% or less of what they eat. I totally agree with that. But if they have quality forage that rule of thumb does not apply.