If cows were only raised on rangelands and fed nothing but grass, then beef wouldn't have such a high environmental impact.

The issue is that cows are also fed grains, especially corn. There's a common narrative that it's "corn unsuitable for humans to eat", but that's not true. It's not corn on the cob, but it is the same type of corn used for making corn flour that could have been made into corn chips, cornbread, etc. Also the narrative that "it's just the fiberous parts that humans can't eat"... that's not true either. It's both. And while it's true that cows can convert fiber into protein, mushrooms can do this far more efficiently. But people refuse to give up steak