Cohen, who based on prior writings and my prior correspondence with her, is a left-winger who likely has a fair amount of sympathy for Sand’s political views, bends over backwards to be “even-handed.”
Nevertheless, if you read Cohen’s piece closely, you see that she gets things basically right: what Sand has to say that is correct (e.g., Jews grew their numbers in part by conversion, that Jews are not ethnically homogenous–no surprise to me with my blued-eyed daughter and blond, blue-eyed grandmother–, and that there was no sudden and complete exile of Jews from the Land of Israel in 70 A.D.) is known to anyone with even a passing interest in the subject. His more “controversial” points (e.g., that Ashkenazic Jews are primarily descended from Turkic Khazars, that Sephardic Jews are primarily descended from Arab invaders who converted, or that the notion of Jewish nationhood was invented by 19th century Zionists) are thinly-veiled, ahistorical, politically motivated lies, contradicted by readily available evidence.
(As a related aside, I recently learned that I’m distantly related to Rashi, the great 12th century commenter on the Torah and Talmud. Rashi lived in France, whereas my ancestors come from Eastern Europe; the Khazars don’t seem to have been involved.)