An interesting point, but a bad way of saying it.

I find it credible that people with different genes could have different optimal diets. How much of those difference would be between different ethnic groups, and how much would be between individuals within the same group, I have no idea. I also have no idea how much "what my ancestors ate" is close to "what would be optimal for me to eat". Also, I have no idea whether a diet optimized for a specific human would be significantly better than a diet optimized for an average human, compared with the improvement we would get by switching from an average first-world diet today.

I would like to see this question answered, preferably by someone who already doesn't have their bottom line written either way.

(A few random thoughts: Food allergies suggest that at least some individuals need wildly different diets than their neighbors. I would expect ethnic group differences in eating dairy products, and in vitamin D requirements. If Soylent becomes popular among people from different ethnic groups, we could get some nice data.)