The Soviet Union was a multinational state, using a multinational apparatus of repression to carry out national killing campaigns. At the time when the NKVD was killing members of national minorities, most of its leading officers were themselves members of national minorities. In 1937 and 1938, NKVD officers, many of whom were of Jewish, Latvian, Polish, or German nationality, were implementing policies of national killing that exceeded anything that Hitler and his SS had (yet) attempted. In carrying out these ethnic massacres, which of course they had to if they wished to preserve their positions and their lives, they comprised an ethic of internationalism, which must have been important to some of them. Then they were killed anyway, as the Terror continued, and usually replaced by Russians.
The Jewish officers who brought the Polish operation to Ukraine and Belarus, such as Izrail Leplevskii, Lev Raikhman, and Boris Berman, were arrested and executed. This was part of a larger trend. When the mass killing of the Great Terror began, about a third of the high-ranking NKVD officers were Jewish by nationality. By the time Stalin brought it to an end on 17 November 1938, about twenty percent of the high-ranking officers were. A year later that figure was less than four percent. The Great Terror could be, and by many would be, blamed on the Jews.
To reason this way was to fall into a Stalinist trap: Stalin certainly understood that Jewish NKVD officers would be a convenient scapegoat for national killing actions, especially after both the Jewish secret policemen and the national elites were dead. In any event, the institutional beneficiaries of the Terror were not Jews or members of other national minorities but Russians who moved up in the ranks. By 1939 Russians (two thirds of the ranking officers) had replaced Jews at the heights of the NKVD, a state of affairs that would become permanent. Russians became an overrepresented national majority; their population share at the heights of the NKVD was greater than their share in the Soviet population generally. The only national minority that was highly overrepresented in the NKVD at the end of the Great Terror were the Georgians—Stalin’s own.
I don’t know. The structure of the argument seems like apologism/justification. It also fails to mention many of the top leaders, like Lazar Kaganovych who masterminded Holodomor.