Sorry but this just isn't true. Of course you need more energy to produce a cow and then eat it than you need to sustain yourself by just eating the cows food.
I think it really depends by what you mean when you say vegan.
If you’re eating vegan cheeses and whatnot you’re probably not doing so hot. Or impossible burgers. Or any other manner of “invented” food that is not essentially basic agrarian or hunter-gatherer.
Conversely, wildlife play important ecological purposes and can be hunted sustainably.
Wild life can also be useful in processing things we cannot eat and grows in abundance (grass) into things we can eat (cows).
