Why do you think that conclusion is 'practically certain'? R1b diffusion in most of continental Europe predates these dates by thousands of years and as the paper notes, there's no evidence of conquest or unified governance across this region in this time period.
How is the extirpation of the indigenous Y haplogroup by immigrant R1b people not evidence of conquest? We’re talking several millenia BP it’s not as though we’re going to find formal declarations of war.
As for the timing, it lines up just fine under the hypotheses based on Reich’s genetic data instead of inaccurate proxies like potsherds.
Are you perhaps mixing up events? "Extirpation of indigenous european haplogroups" is a phrase I'd associate with the WHG/EEF boundary. Clearly we're not talking about that. I don't think I need to point out that extirpation of EEF-associated populations didn't occur either and isn't particularly relevant since one of the main areas these weights were found was Sardinia.
The paper is also talking about a period that begins in the eastern Mediterranean around 3k BCE, moves through southern Europe, and eventually ends up in Northern Europe and Britain around ~1k BCE. It's clearly not associated with WSHs.
