The native American languages were very diverse and yet the vast majority of Amerindian men belong to Y-DNA Q1a3a1. I'm sure there are other examples, but that is the first that comes to mind.
In my opinion that view is too simplistic. The germanics conquered and then created the western europe we still live in so the importance of them is enormous. They have contributed to the western European culture(since the fall of Rome) more than the celts. The continental Celts was culturally marginaliced a long time.