It's always going to be more efficient to feed grain, soy etc. directly to humans than it is to feed those crops to cows then feed cow meat and milk to humans (you lose about 90% of the crop calories creating beef: https://en.wikipedia.org/wiki/Feed_conversion_ratio). People arguing the opposite are usually under the false impression that cows are only fed grass (there's no enough room for this for the amount of cows we need) or arguing corner cases.