Corn fed beef are just fatter. It’s not more nutritional than grass.
I did a little research and cattle are just finished off on grain. For the major portion of their lives they eat grass and other things like the leftovers from distiller’s grains that humans can’t digest.
Only 7% of their overall feed input is grain.
https://extension.okstate.edu/fact-sheets/corn-as-cattle-feed-vs-human-food.html