“LOL! To say the least, the complete (or nearly complete) replacement was unlikely to have been 100% kumbaya. The complete disappearance of those earlier male lines suggests a small initial population, and/or a smaller male population (due to polygamy)”
Not necessarily true.
A. Small only needed to be much smaller than the waves of new settlers.
B. Neither is warfare between settlers and natives out of the question as far as the number of “native” procreating males, or over time, the number of procreating males from the settler population as much much higher due to greater status as part of the new dominant class.
C. Nothing requires that polygamy HAD TO BE part of the reason for a smaller ratio of native males to settler males. The inmigrating population could have been vastly larger.
Polygamy doesn't have to, didn't say that anyway, the point is, it is one possible reason that the earlier male population was too small to withstand the replacement by the newcomers. Since the newcomers definitely did replace them, it probably wasn't just due to differential breeding rates.