Since this is all based on only mito-dna, couldn’t it be that, rather than an invasion/inmigration, the pre-existing Euro-HGers went forth and collected new wimmins thus bringing in a pool of new mito-dna?
Not unheard of.
I've read that the female, mtDNA of Iceland is the same as Ireland. The male, YDNA in Iceland is from the male Vikings.
On the way to Iceland, the Vikings stopped at Ireland and collected the prettiest Irish women and took them to Iceland as wives.
Some have called the women of Iceland the prettiest in the world. The Vikings didn't take any ugly women there.