Cattle agriculture is not cows. It's human beings farming cattle. Also, they are only regenerative under certain conditions. Cows are especially bad in wet soil areas and they can damage the area reducing plant growth through pugging. This can cause soil runoff and flooding. In addition, cattle will displace native flora and fauna.
Indeed my cattle mostly eat weeds, and eat things my chickens can't really eat. I don't feed either of them mass-produced crops, which actually also have ecological consequences in terms of huge amounts of petrochemicals needed both to fuel tractors and combines and to keep fertilising, topsoil losses, the amount of herbicides and pesticides sprayed, and so on.
If the market demands more chicken over beef, producers are perfectly capable of making a switch.
Cows are able to make delicious beef from grass and thistles; that they are often fed other things is not a proof that eating cows is bad.