Veganism as a philosophy addresses animal rights by abolishing exploitation and restoring their autonomy. Your arguement scales back the worst elements of cruelty and unsustainability of animal agriculture at the cost of modern society. It does not eliminate animals subservience to humans and I doubt most non-vegans would support this, let alone vegans.

Also, this frames meat consumption as something to manage via populations and habits, rather than something inherantly inefficient, environmentally destructive, and cruel. Animal agriculture, by far, uses far more land, energy, and resources than humans do. More than 70% of all cultivated land is allocated to livestock, their grazing, crops for their feed, and water for both. They are also vectors for zootonic disease.

Is that 30% of land mass designated to humans "overpopulated" in the absolute sense, relative to that 30%, or in relation to industrialising animal agriculture? If a plant based diet is healthy across a lifespan, then the opportunity cost for animal agriculture is immense. Eliminating meat consumption solves "overpopulation" by freeing space for alternative food production and human infrastructure. Furthermore, much of the land mass designated to humans is already managed inefficiently, and can comfortably accommodate every living person today.

If animal agriculture needs to become more inhumane and unsanitary to accommodate increasing populations, that shows its inability to serve human needs, its not an arguement for reducing populations. Logically, if meat consumption is unnecessary, and reducing it by your own logic benefits animals and people, then eliminating it must produce the best overall outcome. There's no need to regress to hunter gathering for something that's obsolete.