I’m not seeing how it makes “ethnicity” redundant. Ethnicity does not necessarily have anything at all to do with genetics: Merriam-Webster defines “ethnic” as “of or relating to large groups of people classed according to common racial, national, tribal, religious, linguistic, or cultural origin or background.”

As a real-world example, Hispanic is an ethnicity, not a race, and it’s basically useless in DNA terms — Hispanics can descend from the Spanish, from people conquered by the Spanish, from black slaves purchased by the Spanish, or from any combination of them. In other words, they can have different races. These racial categories — the common stock, the partly inbred extended families — are the ones that DNA can determine.