Well, I'd say if this is true then it corresponds well with what I told above: R1b was a North Eurasian . Europe as a whole is part of North Eurasia (the southernmost parts of the continent are as far north as North China) and is directly linked to North Asia with no major and insurmountable barrier (the steppes, even the Urals are not that big a barrier). Even the northern part of West Asia (Caucasus, Black Sea coast, Caspian coast etc.) is an easily reached from North Eurasia.
As for R1b-M269 minus L23 being more concentrated on the Balkans, as you know these inferences are a bit flawed, we can't just presume that the most ancient population carrying the upstream clades of a haplogroup never got completely extinct or completely displaced from their original homeland (I'd say, though, that usually this kind of study allows us to at least establish the broad region where the haplogroup came from, in this case broadly Eastern Europe). I do not dispute that is likely.
But in any case I was talking about R1b as a whole, not such a downstream and specific subclade and M269. I have no strong opinion about the origin of M269, but I'd say, yes, somewhere between the Balkans and the Caspian Sea region (I know, a huge area, but my best guess until more specific data are brought to the table).
However, unlike you, I do believe that L23 in its latest stage before splitting into L51 and Z2103 existed first on the steppes, or at least east of the Carpathians. And I think that all of that happened before the Copper Age and still in early Neolithic or even Mesolithic times, with L51 and Z2103 becoming two different lineages (probably far apart from each other, but still in the same broad region) in the transition from the Late Neolithic to the Chalcolithic. I think these two populations were similar (not identical) autosomally, probably some mix of EHG, CHG and a little EEF, because the Caucasus paper found the "usual" EHG+CHG mix in Pontic-Caspian samples as early as the Early Chalcolithic (estimated 4200 BC).
I see Indo-European languages being spread by both L51 and Z2103 tribes, and I just cannot for now believe in an origin of undivided PIE any earlier than ~4500-4000 BCE, roughly the time when L51 and Z2103 are already supposed to have been distinct lineages. I think the idea these L51 people adopted their centum and in many aspects "archaic" Northwest IE language from the CWC (who are probably associated with the appearance of satem Balto-Slavic and Indo-Iranian centuries later), mixing to form the BB, quite hard to accept. The innovative characteristics of satem languages had probably already developed by the mid Bronze Age, and we'd expect Celto-Italic to be much closer to Balto-Slavic than they are (some glottochronology methods estimated their split to as early as ~3300-3100 BC IIRC).