You're saying it's possible to accurately determine how closely related individuals (and even groups) are.

I agree.

But you can't determine where those individuals' ancestors lived at any given time unless you also have historical data. Land does not imprint upon DNA.

So these companies can tell me that I have many distant cousins in, say, Brazil and Portugal, and we can make an inference that I'm of Portuguese descent. But clear-cut situations like that are extremely rare unless good genealogy records are kept as well and can be combined with genetic testing.