Cows in America derive most of their calories from corn. And while most Montana cows generally live on land unsuitable for crops, Montana only has a small fraction of American cows.
And I believe that your comments are even less true in other prominent cattle producing countries than America.
Grass doesn't grow on hills, or soil with lots of stone/rocks that would be prohibitively expensive to turn into cropland? Not to mention that cropland using regenerative farming, or anything actually sustainable, should include grazing animal rotation.
And I believe that your comments are even less true in other prominent cattle producing countries than America.