OK so you are claiming that it was the case from the Iron Age onwards.
And PIE expansions had been already during the Bronze Age, in times when language was still strongly correlated with Y-DNA, as you admit.
That was Marija Gimbutas, not me. A nice summary of Gimbutas and other archaeologists is provided by Grzegorz Jagodziński here:
http://grzegorj.interiowo.pl/lingwpl/pochie2.html#hip6
Cultures often linked with the earliest/deepest PIE origins according to the Steppe Hypothesis, are either all or just some of these:
- Seroglazovo culture (11th-9th millennia BC)
- Bug-Dnieper culture (6300-5500 BC)
- Dnieper-Donets culture (5400-4200 BC)
- Samara culture (6th-5th millennia BC)
After that, in the mid-6th millennium BC, that early PIE population emigrated towards the Middle Volga, and formed Samara culture there. The reason of that migration was probably the great flooding of the Black Sea by water from the Mediterranean Sea (which took place ca. 5600 BC) - as the result of which water level in the Black Sea rised by even 150 meters and large areas of previously dry land became part of the Black Sea. In their new homeland at the Middle Volga, PIE gradually learned from their neighbours to the east and to the south about the domestication of horses and about copper metallurgy. In 5200-4000 BC Khvalynsk culture existed between Saratov, Northern Caucasus, the Azov Sea and the Ural River.
Khvalynsk culture was a continuation of Samara culture and a predecessor of fully developed kurgan cultures from later times. It was a Copper Age culture. They had domesticated horses. Proto-kurgans also emerged already in the Khvalynsk culture. Around 4500/4200 BC people of Khvalynsk culture started to expand westward (Phase I of PIE expansions according to Gimbutas), forming Sredni Stog culture (4500/4200 - 3300 BC). Sredni Stog people established contact with people of agricultural Cucuteni-Trypillian culture (5500–2750 BC) from Romania, Moldova and Ukraine.
During the existence of Sredni Stog culture,
PIE dialect continuum gradually started to split into various IE language families.
The earliest group which split from PIE of Sredni Stog culture, were Proto-Anatolian speakers of Cernavodă culture (4000-3200 BC). Around 3300 BC two other cultures - Yamnaya (Phase A) and Corded Ware (Middle Dnieper = Early Corded Ware) - emerged from Sredni Stog.