vegan

it’s harder to fight evolution and it takes time

See, I don't really understand why you think we would need any evolution for this. For what it's worth, we are already very well capable of thriving on a plant-exclusive diet with our current genetic setup.

meat free lifestyles would most likely push different evolutionary traits in a few million years

Most probably not - or at least not to great extent. You need a selection pressure for evolution to happen. I.e. you need natural selection. And since our food-choices influence our chances for reproduction very little in our modern days. Humans removed them selves to a great extent form "evolution by natural selection" anyways in our age.

you have to consider cultural influences as well

Cultural influences can be used as an explanation for a status quo, but are a bad justification for future behavior most of the time.

Additionally, veganism is more prominent in higher income countries because of food processing and “health food” taxes cost money, so many vegan items aren’t inexspensive.

I can not agree with you on that statement in any way. The cheapest staple foods you could get are mostly vegan (Grains, Legumes, Dried goods, seeds, vegies, fruit, potatos). Meat and animal products are quite expensive to produce in comparison. Most of the time this just does not seem like it, because animal ag is extremly subsidized to keep this industry economically viable. If anyone would need to pay the FULL price of animal products, most of us would not be able to afford then on a regular basis.

Those people that are too impoverished to afford a full vegan diet would starve without meat.

Completely backwards. "Poorer" regions that have a climate suited to produce crops often have traditionally a very plant heavy diet, since things like grains and legumes have a great shelf life and are very cheap. Meat is fucking expensive. It boils down to basic thermodynamics. You need to put so much calories into an animal that you will never be ably to retrieve by consuming their body. It is wasteful.

Also consider those places where the land can’t be fertilized and farmed. Those people as well would starve.

No one in their right minds would say that some indigenous tribes or the Inuit need to be eating veggie burgers tomorrow. We are talking about the vast majority of people on this planet - like you and me. And we have the choice. Diverting the argument over to some hypothetical about foreign tribes or poor people is not necessary and also not at the heart of the arguments.