The kinds of stuff Hancock advocates like globespanning ancient civilizations obviously don't show up in the genetic record, but some ideas that used to be pretty far out like "widespread admixture between AMH and neanderthals" are widely accepted today on the strength of the genetic evidence and other research that was done to back them up.
Washing up in Iraq, India, Mexico, and Peru would be more consistent with a single origin in southeast Asia than in the Atlantic, but a global cataclysm ought to produce refugees from multiple places.
Any genetic signal of scattered refugees would be faint.
1. Genetic findings among South-East Asians indicate that the maritime powers of India (and mostly south India) were of greater significance at their peak than the Delhi sultanate or the Delhi centric view held by most historians. [1][2]
2. We are expecting huge changes to our understanding of ancient humans in Africa [3]
3. The most famous co-evolution fact of milk-and-lactose-tolerance might not be true [4][5]
4. The so-called-indo-aryans might not have brought the caste system or "Indian culture" with them. The Dravidians are almost just as "indo-aryan" as their non-Dravidian counter parts and the Aryan-Invasion-Theory, might not have had an invasion to speak of at all. [6][7]
These are extreme simplifications of the interesting stuff I found that was relevant to my country. I'm sure there is just as much about every other culture and it's just as spicy. Also, emphasis on 'might' & 'probably'. These fields are mid-disruption, and facts on the ground are changing as we speak.
[1] https://www.gnxp.com/WordPress/2018/10/06/likely-male-mediat...
[2] https://www.gnxp.com/WordPress/2018/09/20/indic-civilization...
[3] https://www.gnxp.com/WordPress/2021/02/03/so-many-assumption...
[4] https://www.gnxp.com/WordPress/2021/01/28/got-milk-long-befo...
[5] https://www.science.org/content/article/humans-were-drinking...
[6] https://www.gnxp.com/WordPress/2019/09/12/the-aryan-integrat...
[7] https://www.gnxp.com/WordPress/2022/08/15/indra-is-absolved-...