I understand your argument, and there are regions where meat is the only viable option given the lack of arable land. That being said, I've been a vegetarian my entire life and have a much more nutritionally complete diet than most (if not all) of my meat-eating friends...and the truth is growing plants to eat directly is much more efficient than raising animals, because animals require significantly more land and water to grow, pollute our waterways with their waste, and are the primary causes of deforestation in the world. All those rainforests we've cut down to grow soybeans and corn? Those are going primarily to feed cows...if we just ate them ourselves we would need much less land to grow them. In fact, beef production uses about 60% of agricultural land while producing only 2% of global calories consumed. So we'd have more food and resources for everyone if we ate less meat, especially big mammals (cows/lambs/pigs).

(Source: https://www.ucsusa.org/resources/grade-choice#:~:text=Nearly%2060%20percent%20of%20the,kilometers%20of%20land%20to%20produce.)