You're comparing two cases of "mass production" without any quantifier.
Beef has an over 15 times larger carbon footprint compared to tofu.
https://ourworldindata.org/environmental-impacts-of-food
So sure, if everyone switches we would substitute one mass production for another, but we could feed 15 times as many people (all else equal).
I haven't ran the numbers, but parent hinted at a cow needing to eat, say, 10 Kg of soy per Kg of meat produced, while you could have just eaten the soy directly.
Meat production uses a lot of land to produce food for your food, that's why it's so inneficient. Instead you could just use a tiny fraction of that land, and grow enough food for everyone.