Race of course is trivial to Faith
Which is why God Himself ordained that He be born in the flesh of a particular race with a specific bloodline...
If race is so trivial, why not just be born of a Babylonian?
He was born of a specific bloodline because of the promise to Abraham.
There was plenty "mixing" along the way. The genealogies make note of all the gentiles in the bloodline.
This "race" is defined by particular men, Abraham (Isaac and Jacob) and David. And it is central to a promise and many prophecies. You, in making that argument, might want to point out Adam and Eve, the first humans, who are the parents of all humans.
Unless you are thinking people here are somehow part of Messianic prophecy, that comparison does not make sense, and in fact, defends "mixing".
Races are accidents. They are just something which arises out of geographical boundaries and get reinforced over time.
There is nothing particular about them.
While we have fixed notions on common "races", it is a convention based on perception.
There are stable and old populations in Africa of "black" people who have straight hair, and even one which has blond hair. Some have epicanthic folds ("Chinese eyes"). All sorts of heights are reached. This is just in Africa, in African populations without "mixing" in recent times. There is no "black race". There are "black" people in southern India who are as distinct from black Africans as white Norwegians, despite having a similar skin colour.
And what about people who are already "mixed"? Who should they marry? Other "mixed" people?
A big danger to those living the Faith is becoming enamored by the things which happen to be around oneself, rather than seeing what matters. What a small mind opens its eyes, looks around, and thinks it beholds eternity.