Doug McCallum, I'm with ya. Other reputable genealogical DNA authorities include Jim Bartlett, Blaine Bettinger, Kitty Cooper, Debbie Kennett, Leah Larkin, and many more.
I shudder. We have many new millions engaging in DNA testing for the first time, and advertising companies, of all sources, have led them to believe that the 0.023% sample provided of their overall DNA will result in explicit, unequivocal results explaining their ethnicity and heritage.
It won't. Within the current constraints of the technology, it can't. It can tell you if you posses Neanderthal DNA, which if you're of European descent you almost certainly do, but it can't tell you definitively if you're Greek or Italian, or much less from County Cork, Ireland or Kirkcudbrightshire, Scotland. Consider that the Norse circa 1,100 years ago ranged from Iceland to Ireland to the Straits of Gilbraltar to the Mediterranean. I can't count the number of people absolutely shocked to find "Scandinavian" in their DNA.
Contemporary evidence is showing that we, as a species, moved about far more than was believed even just a decade ago. And we moved about far earlier than previously thought. There were no simple and discrete and tidy migrations out of Africa, and then from the Caucasus into Europe or the Levant into East Asia. Didn't happen. Humans are not the rational, organized beings we might believe them to be: ancient human migrations were sporadic, random, and opportunistic, not logical, planned, and structured.
And the video? "Identical" twins is subjective; there is no evidence these were monozygotic twins. The stipulation for genetic similarity...and even then, it's known that monozygotic twins can still differ in copy number variants. My general opinion on ethnicity results here: https://casestone.com/threlkeld/blog/93-should-you-trade-your-lederhosen-for-a-kilt.
And there are many who feel they fully understand genetics and genealogy: https://casestone.com/threlkeld/blog/112-genetic-genealogy-and-the-dunning-kruger-effect. I'll posit only a small fraction of those who think they understand DNA actually do. I confess that I certainly do not, but I've offered on occasion to give an extemporaneous, real-time, oral quiz to some self-proclaimed "experts," and never have been taken up on that offer.
Leave the ethnicity and admixture to the PhDs who study population genetics for a living. Read David Reich's 2018 book. Studies of deep ancestry and anthropology have little or nothing to do with genealogy.
Our common, cheap, direct-to-consumer tests are highly reliable in doing what they do: identifying an allele associated with a specific locus on a chromosome, a SNP. That's what the tests do. Take a squishy, tiny, biological marker and convert it to a digital element that we can read and compare.
The microarray genotyping process doesn't have anything to do with ethnicity or heritage. That's what the marketing-driven testing companies struggle to do with the data after the test is completed. When it's all about what-ifs and comparisons against whatever particular database they're using on the day.
I love that AncestryDNA's marketing campaigns have brought many millions to DNA testing. I hate that the same marketing has given them false impressions about the purpose and usefulness of those tests.
Let's please not confuse the science of DNA testing with ethnicity smoke-and-mirrors guesswork.