>The American melting pot works well (or worked well) because it was a nation made up from a blank canvas with no prior historically established dominant ethnicity

That's a bit of an oversimplification. They were British colonies for well over 100 years before declaring independence. The US Census website states:

"Not surprisingly, the first census reported that based on the names of heads of families, more than 90% of the White population in 1790 hailed from British stock: English (83.5%), Scottish (6.7%) and Irish (1.6%)."

https://www.census.gov/library/stories/2023/12/boston-tea-pa...

>And even at that was built on first disenfranchizing (to put it midly) the natives.

Not many European colonial powers purchased land from natives the way the US did. For example, considering the Louisiana Purchase area, the US paid over 20x as much to natives living in that area as the US paid to France:

https://www.slate.com/articles/news_and_politics/history/201...

The US looks bad compared with a hypothetical (nonexistent) perfect country. But compared with European powers, it looks pretty good.