I wonder who used similar language some 80-90 years ago

ah, the classic "Russians are actually Mongols" argument

also, in this fantasy scenario, how the hell did the Ukrainians avoid mixing? A bunch of modern Ukraine was also conquered by the Mongols, and even before that, the Pontic-Caspian steppe has lended itself very well to various other steppe peoples, like the Alans, Bulgars, Khazars, Pechenegs, Cumans, Kipchaks... If you're so mad about the steppe influence, might as well hand eastern and southern Ukraine over to the Russians, that land clearly shouldn't be in pure and unbesmirched Ukraine.