You say race is based on skin pigmentation. But it's also based on eye shapes, and many other genetic markers. It isn't a false construct, it is rooted in biology and anthropology.

It is certainly as real a construct as the cultural aspects of being part of one (or more) of a world culture with all of its histories, traditions, customs, mores.

This is not to say one race or culture is superior to another. To look at this, look at fitness. How well is a race or culture fit to their environment? How well are they able to adapt to a new environment?

I'll let others answer those questions for themselves, but I would also state that there is no assumption that multiracial or multicultural is more or less well adapted or fit to an environment.

I think there has been quite a bit of cultural arbitrage happening over the last few centuries, as travel became easier and less costly. I would say that any racial arbitrage would have to occur over a much longer time period..