Earlier quoted context omitted.
Huh? Vegetarian/Vegan diets use a fraction of the land compared to a omnivores diet. https://ourworldindata.org/land-use-diets
That land is called marginal land, or pasture. You can't grow crops there economically r do anything else really. Removing the grazing animals from the land changes nothing and does not improve the environment at all. That land would be worthless if not for grazing animals. I'm not sure there is enough arible land to support the human population without grazing animals. I suspect anything is possible with enough tech…
One third of all pasture is suitable for growing crops.
Removing grazing animals from the land can allow for reforestation and increase biodiversity and carbon sequestration.