Since this question always comes up at some point, I decided to do a rough back-of-the-envelope calculation of the % steppe across the Indian subcontinent. The way I did it was by taking Pakistan, Bangladesh, and India, and estimating the average percentage from the caste breakdowns (e.g., UP is 20% “upper caste” and 20% “Dalit” and 60% neither, with fractions of steppe/Sintashta about 30%, 10%, and 15%, respectively).
So the final number I came back is that 14% of the ancestry in modern-day South Asia is from the steppe in the form of people descended from Sintashta pastoralists. That is about 220 million human beings worth. You can judge whether that’s significant or not. Additionally, it looks like closer to 20-25% of the Y chromosomes are derived from these people.
I’m not “showing my work” because I think no matter how you estimate it, you’ll get a number in this range. Perhaps 12%. Perhaps 16%. But what difference does that make?