It is a matter of degree. If you look at the diagram I shared, many of us founding stock Americans are Celto-Germanic because much of England, Ireland, and France are that. We are still Nordic and Europid. This close sub race mixing proved beneficial as seen in the stock and its cultural outcomes.
Generally the more distant the mixing, the worse the outcome. Occasionally, some of these mongrels come out OK, and the jewish media puts them on stage to distort our perception. Southern Italy, Egypt, Mexico, Brazil.. are largely mongrel populations. Nothing great comes out of those places anymore.