Except its use as pasture has wrecked the ecosystem that would be there otherwise. From forcing certain plant life to driving out predators, "would still be grass" isn't really saying much when the damage is severe nonetheless.

Yes, you are right, for pastures. The category Lifestock feed is soybean, corn, wheat, barley and triticale, all that goes into the stomachs of monogastric animals (pigs, poultry, ... humans).