Lets take a cultured plant of wheat from family Poaceae: There is a crop of seeds once in the year and then the plant die. The cow eats the grain and maybe they eat the straw also. Finished.
Now lets take a similar plant in a pasture or a meadow. But the cows aren't put there for the "once in the year" grain of this plants. Is the Poaceae superpower to grow leaves again and again after being grazed what counts.
Therefore we need to take in mind that we can extract more food from the same plant in a pasture, and this happens all around the year.
And not all fields are flat. Some are located in mountains and have inclinations of 60-70 degrees or so. You can't use machines there to sow or harvest. Would be economically unfeasible. Using this areas as grazing fields for goats or sheeps are a better option.
And there are the arid areas, where you have all the sun and space to culture, but none of the needed water; and where a lot of plants are poisonous or have horrid spines. If you remove the donkeys, goats and sheep, you can't have still tofu in return. Does not work like that.
We need to refine our master plan of "1 Kg of meat equals to 10 of wheat". For some places "1 Kg of meat equals to 0 Kg of wheat".
Of course if "we'll do it for the animals", a meadow inhabited by 450 species is much better than a concrete parking; and the later holds still more species than a monoculture of soybean. All soybeans means "no more butterflies, micromammals, flowers, and birds"