> Just to be clear, the Indo European migration is presumed to be a trade/culture migration
Not the case. You're making the "pots, not people" case, which ancient DNA evidence has thoroughly debunked. Changes in material culture usually do indicate large-scale population movements. Yamnaya remains from the Caucuses, for example, are genetically almost identical to the ones buried in the Corded Ware culture that spread through Europe ~5000 years before present. The Yamnaya, a steppe people, completely overran Europe, and today, contribute just over 50% of the ancestry of Western European populations and who spread Indo-European languages there and elsewhere.
The idea that prehistory was full of peace, love, and gradual and voluntary cultural change is ridiculous and indefensible, especially in light of modern genetic evidence, but also on the grounds of common sense.
Why wouldn't you expect to see large scale folk migrations? We have historical records of large-scale movements (e.g., Germanic tribes from Tacitus), and one would expect similar movements, of even greater scope and intensity, to have occurred in prehistory. This kind of movement was the norm, not the exception, in prehistory.
Post-1970s thought in this area seriously annoys me. It presumes a gradual, peaceful transition everywhere at all times despite stark evidence to the contrary. Read Ward-Perkins for a good rant on how fellow historians believe, against all historical and archaeological evidence, that Rome never fell. He's as frustrated and baffled by this thinking as I am.