First of all, they were not unskilled savages by any means, but had their advantages. Secondly, most civilisations became weak over time, and prey to more warlike pastoralists, which had a better demography and cohesion, were more flexible, among other things. And that doesn't apply to IE only, but e.g. Semites too.
I agree with the bolded comment.
As to being more "flexible", that I don't see. People adapt to their environment. The Natufian hunter-gatherers adapted to an environment where there was plenty. They were smart enough to figure out that they could store the grains from plants in their environment, then plant them in suitable nearby areas, then domesticate the animals in their vicinity.
People living in an environment hostile to agriculture lived on hunting and fishing. When they traded furs, perhaps, for goods from farmers they realized they could trade for these animals which could probably live off the steppe grass.
It's as simple as that.
The farmers of the Balkans were "flexible" and smart enough to realize that maybe they could use naturally occurring ores to make ornaments, then tools, then they were flexible enough to experiment with combining the ores. The steppe people just traded for metal goods. Eventually they did try to copy them, but the original attempts were very primitive.
Humans adapt or die.
As for turning to pastoralism when agriculture failed, I'm sure you're aware that there's quite a bit of literature indicating that actually, pastoralism was first attempted by farmers and it spread from them to the steppe.
In fact, I'm hard pressed to think what the steppe people "invented", other than piling their goods on carts and going to the new pastures versus transhumanism as practiced by farmers to this day. That, and the "real" advantage, the domestication of the horse.