thats false
seperation occured in east asia
if CA was never destroyed by the Mongols, modern day CA would look like a whiter version of Georgia, Armenia, Azerbaijan, Osetia.
The Yuezhi, believed to be Tocharians, were living in central China since ancient times, until the nomadic Asian xiongnu came and genocided them and the survivors escaped to the east.
Tocharians are more similar to Germanics, Celtics, Latins than to even Slavs and Indo-Iranians. It's basically like there was a western european country inside the modern border of China.
Even today, R1b, a marker of Centum Aryan group, is found in relatively high frequency among Uighurs, but largely absent from CA further to the west.
en.wikipedia.org
The Scythians on the other hand, occupied the steppes including Mongolia
The first Asian nomads, were believed to be from Manchuria, or Northeast China, they were forest dwellers.
My theory is after the contact with the steppe nomad Scythians, the Turkic gooks living in forest adopted that nomad lifestyle, and due to their bruthal and ruthlessness, gradually genocided Scythaisn and eventually led to their extinction.
It's hard to imagine, but the steppe was fully INDO EUROPEAN, from europe all the way to mongolia. Then the gooks stole the tech and over thousands of years pushed all the way from mongolia to europe.