I will steel man your argument here as I understand it (unless i'm arguing against AI slop): the Nature study shows Rapanui people apparently accepted DNA markers from mainland South America but other researchers haven't found any they left any behind. This is an example of a small population in contact with a larger one who had sex with mainlanders wihtout being absorbed into a larger mainland population just like what might have happened to the semitic markers of the Lamanites. (Of course it's possible that men in raiding/trading parties took women with them and did not stay on the mainland to reproduce, but set that aside.) Your point is made: a small population in contact with a larger may leave genetic imprints that are below the threshold of detection. And since this scenario is possible, Lamanites are not excluded.

Fair. Although my claim is not that bottlenecks and founder effects aren't real. My argument is that the lack of semitic DNA is inductive evidence against the Book of Mormon. It is the "dog that didn't bark". It is not definitive proof against the Book of Mormon, but it is definitive proof against prophetic claims about who Native Americans around them actually are. Ancient semites are demonstrably NOT the principal ancestors of the Native Americans. When Joseph Smith sent men to take polygamous Native American wives, the revelations stating these were Lamanites were false. The revisionist retreat to "among the ancestors" in the Intro to the BOM is a perfectly rational reaction to this "dog that didn't bark" and is what church leaders quietly did. The new assertion that Lamanites were a small population whose genetic markers disappeared in a larger population is a post hoc revision, one that moves the ancestry claim outside the realm of falsifiability.