And we need to eat many pounds of cow.

Or many more pounds of plants to generate a pound.

Plants to animal to you is 10% efficiency. That cow needs to eat 10 lbs of plant to get the nutrients you’d get from 1 lb.

Except you couldn't extract any nutrients at all from the plant matter the cow is eating, no matter how much of it you ate.

Not everyone is allergic to corn and wheat.

People don't eat efficiency. They want nutritious and delicious food. No one's mouth waters over kale.

We're lucky that kale isn't the only plant-based option. The vegan culinary tradition has existed for centuries. Seitan was invented as early as the 6th century in China.[0] And western vegan culinary traditions have evolved rapidly in the last 10-20 years. The reduction of plant-based diets to just eating salad is not grounded in the reality of those who are plant-based.

[0]: https://en.wikipedia.org/wiki/Wheat_gluten_(food)

The way cows get plant matter is a lot less environmentally costly than the way humans get plant matter. Their standards are a lot lower than ours. Humans don't like to eat scrub-brush and corn husks.