Actually there is a difference in meat structure. It’s easy to tell if someone is lying about it being 100 percent grass fed. Corn and grain create a fat that is denser and more pronounced throughout the carcass vs grass fed.
That said, the difference in a cooked product is really in the cooked weight loss from the uncooked weight. Sure, the fat content per gram is slightly less and thus a leaner product, but it’s not majorly significant.
the biggest difference is time to market. Corn and grain fed cattle can make it to market MUCH quicker, in as little as 10 months to market weight, which is 1000-1500 pounds, And generally are heavier pound per age than grass fed. Grass fed it’s about 18 to 24 months to market weight, depending on the types of grass/hay fed.