These same "experts" even go so far as to claim to be able to tie specific haplogroups to languages, tribes, and epochs. They will make broad statements, like, "all of Europe was populated by [this haplogroup or that], which represented the [Cro-Magnons or whatever], until they were replaced, en masse, by the [new Haplogroup.]"
(Often the dominant invader haplogroup in their theories tends to be the one of the posting "expert," but that's just coincidence, I'm sure.)
Contrasting these experts are some bona fide theoreticians, who point out that we have less than 100 samples of Caucasian Ancient DNA, and that a simple cultural fact, for example, if one tribe cremated their dead and another tribe buried their dead, could contribute to the number of ancient skeletons that make it to the present day.
So, what I decided to do was to plot the confirmed ancient NR Y Chromosome haplogroup samples on a map, to show whatever it shows.
What I discovered was a complete lack of any real patterns. In other words, it's too early to tell. We need way more aDNA.
I used the excellent data from Ancestral Journeys. All maps are labeled. All times and locations are approximate. All maps are copyrighted, but feel free to share, as long as you link to this page or attribute to me. (The final map is not mine, but purports to represent modern majorities).
What other theories can be questioned by these maps?