American diets are obscene, but in terms of carrying capacity and ecology, a mildly omnivore diet still feeds more people than a vegan diet, due to the presence of land that is unsuitable for cultivation, in-between periods of dry/cold weather where crops struggle to grow, etc

Also consider the pests that cropland attracts, which under a holistic pre-colonial agriculture mode (which produces more calories per acre at the expense of more human labor required), would have often been dealt with through killing (and eating)

https://i.postimg.cc/Hs3NchBJ/y54eh6t6f.png

https://online.ucpress.edu/elementa/article/doi/10.12952/journal.elementa.000116/112904/Carrying-capacity-of-U-S-agricultural-land-Ten

Basically, a sustainable omnivore diet would have less meat, a lot less beef, and more varied sources of meat (possum, raccoon, etc)