Lewontin is a pretty famous scientist. He’s won lots of awards, held influential positions in academia, and so on. He studied at Columbia University, which was home to the Frankfurt School and the father of race denialism himself, Franz Boas. Columbia was the original Western Marxist indoctrination center in America and was responsible for educating many influential globalists, including leading UN figures.
To claim that a “low” Fst rating invalidates humanity’s distinct subspecies would require us to declare countless other subspecies as “biologically invalid.” But you’ll never hear Marxoid academics arguing in favor of that. Their only qualms are with human taxonomy because it obstructs the race-blind globalism that is central to their ideology.
Lewontin’s methodology was criticized by multiple scientists almost immediately after his paper was published. His Fst analysis used 17 individual genetic markers. However, to paint an accurate genetic picture of human races (or any organism in existence), multiple genetic markers must be used in unison. The more markers you use, the more accurate a picture you paint. Additionally, the more markers you use, the less likely you are to genetically misidentify races. Once enough markers are used, the probability of genetically misidentifying an individual drops to below 1% — almost zero.