Well, it doesn't seem that Emp is actually believing this guy, he just says that the man had some good arguments. Am I right?
Yes that is right.

The main point I am making is that history is very much open to interpretation given we don't know all of the facts about exactly what went on, especially given the destruction of the Roman Empire.

But my point is that history such as the Anglo-Saxons & the Celts is deeply intwined with the founding of present day nations, such as England, Wales and Scotland, and it arouses deep nationalistic passions.

We start to move into the area of national myth and claims on racial bloodlines.