Well then lets no plant Barley to feed humans, let's use something else. The thing is a good portion of the surface of the Earth is covered with agricultural fields, most of them aimed at feeding cattle, not humans.

It's a bit insane if we think about it. I doubt that conversion from barley to chicken is so efficient. There is more nutrition in barley than the protein, there are carbs as well and fiber and micro nutrients that would be good for humans, besides only the protein.

A better comparison would be in calories, considering the waste of slaughtering the chicken and all the parts with don't eat, plus all the waste produced by the chicken and the water used.