Cattle doesn’t convert plant based protein into animal protein. Also cattle eats crop that humans can’t eat and which grows in significantly more tough conditions than those required for crops used as feed.
Eating lots of soy is not healthy.
It’s a very weird and unconvincing argument on your part, to suggest humans should just start eating crops fed to cattle and that would somehow work in terms of sufficiently healthy and available nutrition as well as being net positive on climate change.
Cattle eats grass which grows everywhere in the world and cattle produces vastly healthier and nutritious profile of fat, protein, vitamins and other essential nutrients than what you could achieve by growing human edible crops for similar price. Sure you can achieve good nutrition with other expensive vegetables but that’s not what will happen if humans stop eating cattle. Let’s be realistic.