It doesn't just defy plausibility, it defies the actual evidence. We're lucky enough to have an example in the historical record where technologies like the whe

It doesn't just defy plausibility, it defies the actual evidence. We're lucky enough to have an example in the historical record where technologies like the wheel and domestication of the horse were introduced (mostly) peacefully to a cultural context of foragers almost but not entirely unlike Old Europe - and (needless to say) we do not see the sort of Y-haplotype replacement that shows up in the molecular-level data. So the PIE expansion must have involved a lot more conflict than we might guess absent that evidence!