I am pretty sure that what you are describing about the MRH is a little off, but I might just be misunderstanding you. If I understand you, you seem to be suggesting that the MRH is saying parallel evolution occured
without any gene flow. But, anyways, I hope you will forgive me if I have misunderstood
.
The MRH proposes that there was enough genetic flow between the populations that they all evolved together into H. sapiens, with local variation in populations. I guess my best analogy would be ring species that maintain enough gene flow that cladogenesis is kept from happening. Iirc it is essentially saying modern humans evolved through anagenesis.
Here is the image I was taught, as regards the MRH hypothesis.
(Note the "gene flow" across "species")
P.S. I personally have a hard time with the hypothesis, but I have a hard time with the 'strict' OOA as well. Clifford Jolly did some research on hybrid zones between baboon species that had diverged something like 2 million years (i don't recall the exact timeframe but it was quite large) but were still capable of fertile interbreeding. Taken together with the patterns of migration evidenced by the fossils we've found over Europe, Asia, and the Middle East, it seems to me that some amount of gene flow is likely to have taken place, even between species seperated by 100's of thousands of years.