Well, if we’re talking pure food-production efficiency, then if the land is capable of growing grain then it’s probably better to grow grain there and feed the grain directly to humans.

Well in that case perhaps we should do just algae and worms.

Or maybe we should consider more than “pure food-production efficiency” in such a crude manner.

Perhaps we should consider nutrition and health (of those eating the food, and the environment), more than just crude bulk quantity.

Grain based diet would ruin our immune systems, and the health of the soil, without animal fertilizer.