One of the big stories of 19th-20th century population movement is in Europe is the consolidation of ethnically homogeneous populations. “Even today” is imagining the last 30 years not strong desires of the last 150 years.

But let's discount all of this, it might be historical fluke. But even so, the burden of proof is on those proposing alternate hypothesis, people like you and certain bloggers. Without such evidence the null hypothesis stands.

I mean this was a fairly “big controversy” at the time. You can find the arguments floating around the internet that he’s gesturing towards. At this point no one can claim a critique of the null hypothesis hasn’t been proffered.

The critical question always revolves around the meta question of what is the specific framing you need an answer for and what is the “so what” implication that follows the answer.