My understanding of using mitochondrial dna was that there were fewer, and they're easier to map. That came from 23. I'm not familiar with a mutation rate premise. Because of my source I'm familiar with the geographical visual of movement.

Example :

https://www.researchgate.net/figure/Diagram-of-the-migratory-history-of-the-human-mtDNA-haplogroups-Homo-sapiens-mtDNAs_fig2_258254145

This would not be a steady rate because the different areas merging wouldn't be a steady rate. Migration doesn't work that way. The theory you're familiar with seems the opposite of the one I'm familiar with. Do you have any information I can read about it?

Edit : The Seven Daughters of Eve. I have read the book, because it's heavily cited.

http://www.acsu.buffalo.edu/~insrisg/bookmarks/bk01/0920eve.htm