Today's chickens have more muscle mass. They are bred for this trait.

Are you arguing this larger muscle isn't made of protein? What is it made out of then?

Are you arguing these chickens somehow survive without the nutrients that others chickens need to live? How is that possible?

Those are some pretty tall claims you need to back up.

Are you implying that malnutrition or a nutrient deficiency results in immediate death? Death quicker than the 50 days it takes to butcher the chicken?

Are you implying farmers raise these fast-growing, extra-large birds through "malnutrition and nutrient deficiency"?

Yes, I am. Because I am active in the weightlifting community, I'm aware that muscle size has absolutely no correlation with nutrition or micronutrients beyond protein intake. This is extremely obvious if you ever took steroids, because you can become huge eating McDonald's and instant noodle, but even without them the same effect is observed.

So you're saying it's possible to gain massive muscle mass while being, to quote you - "malnourished and having nutrient deficiencies"?

Yes, it is. Nutrition is more than calories. Just as you can become obese with nutrient deficiencies, you can also become muscular with them.