The intersection of nationalism and archaeology can get _really_ weird, and depending on how deep in they are, well, you're probably not going to convince them. If nothing else, it's likely _emotionally_ important to them in a way that it probably isn't for you, the contrived nationalistic narrative being part of, essentially, a belief system.
For a particularly extreme example of this, see Great Zimbabwe, a ruined city in what is now Zimbabwe. When the country was Northern Rhodesia (a white minority ultra-nationalist breakaway state, somewhat like apartheid South Africa but moreso), any serious discussion of the nature of the site was essentially _illegal_ there, because its existence challenged the official narrative (the government insisted that it could not have been built by black people).
It wasn't illegal. The official interpretation however, was that it was not built by locals. Any other opinion was considered "fringe". Which was ironic. Since local origin of these buildings was pretty much consensus among historians before Rhodesia was even a thing.
Then again. Rhodesia didn't last very long. And nobody outside cared much what they thought.
> The intersection of nationalism and archaeology can get _really_ weird, and depending on how deep in they are
A lot of political mythology is based on a group of people being either ethnically homogeneous or ethnically non-homogeneous.
For example a lot of Nazi ideology would've been undermined if it could've been shown that Germans were ethnically non-homogeneous. However it would've been supported if it could've been shown that other groups of people like WW1 German Army deserters were ethnically homogeneous. Or undermined again if there were non-German ethnic homogeneity in WW1 heroes who participated in the German army.
For a particularly extreme example of this, see Great Zimbabwe, a ruined city in what is now Zimbabwe. When the country was Northern Rhodesia (a white minority ultra-nationalist breakaway state, somewhat like apartheid South Africa but moreso), any serious discussion of the nature of the site was essentially _illegal_ there, because its existence challenged the official narrative (the government insisted that it could not have been built by black people).