>2) Most of the places where cows graze grass can NOT support human eatable plant food growing. Only grass can grow there, not eg corn or some grains.

This is completely wrong. You can grow regular crops there but usually the land is sloped, the terrain itself is inaccessible or inconvenient for machinery. There are plenty of Asian countries that do terraced rice farming but this requires massive amounts of manual labor compared to a nice, level and flat piece of land on which tractors and combines can drive on.