We know mtDNA U originated somewhere in western Eurasia and most of the causes that create western ancestry probably existed in very early members of mtDNA U(like MA1 and the Upper Palaeolithic ancestors of Mesolithic Europeans) so it should be considered a west Eurasian maternal lineage.
U5 is the most European of all maternal lineages. We shouldn't question that theory until something like 3 basal U5 subclades dating before the LGM are found outside of Europe. We know U5 originated around Europe because U5 is by far most diverse in Europe, U5 outside of Europe is obviously derived of European U5, and because of ancient mtDNA samples(.
U5 has already been found in multiple major Upper Palaeolithic European cultures stretching a time frame of 20,000 years!!! This is very old knowledge,
U5 has been found in two 31,155YBP individuals from the Gravettian culture, one 20,000-17,000YBP individual from the Solutrian culture, one 12,300YBP individual from the Magdalenian culture, and was the dominate maternal lineage of Upper Palaeolithic, Mesolithic, and Neolithic European hunter gatherers with samples with a very large east to west range; from England and Spain-Germany and Sweden-Lithuania and Russia-irkutsk Siberia(European admixture), south-north range; from Motala Sweden and Karelia Russia-Germany and Poland-Southern Italy and Spain. U5 samples from Mesolithic and Upper Palaeolithic Europe have more U5 diversity than pretty much any modern non-European population. The fact that U5 was the dominate maternal lineage in Mesolithic hunter gatherers of Europe who's blood today is almost completely exclusive to Europe, is even more evidence U5 originated in or near the region we call Europe.
I have heard that the two U5s from the Gravettian culture were ancestral to U5a'b, and used to be called pre-U5. How would they know this unless the samples got results in more than just HVR1 and HVR2? It is very important we know the answer because if it is not true it will cause people to underestimate the age of U5.