Your first paragraph is a bog-standard caveat in the historical study of particular peoples, and you are interpreting it wrongly to see it as a sign of nationalist squabbles among anyone living today. As for the second:

> old German nationalist and even Nazi influences

Notice how the key word there is "old". Scholars may respond to earlier schools of thought in the field, from a now long-vanished time when anyone actually was invested in it for nationalist reasons, but that doesn't mean anyone today is invested in it. For example, major work today on Gothic linguistics, one component in the Urheimat debate, happens in places like Leiden and UCLA where no one has any nationalist dog in the fight.