1) Yes, I also do not think it came from Iberia directly, rather I think it is more likely that both Iberia and Italy were impacted by the same influx that probably came from France via Rhine Bell Beaker-derived cultures. In my opinion it is possible that those "uncertain" languages like Lusitanian, Ligurian, Venetic and Siculian are the remnants of this first wave of "R1b-L51" BB-derived Indo-European, though relative re-convergence to Celtic and/or Italic may have happened during the Iron Age (not very different from how Galician, Leonese, Aragonese and other Iberian languages clearly converged slowly to become more Castillian-like, or Bokmal Norwegian became clearly Danish-like after centuries of influence).
2) I don't know if I understood your point very well, but do you think that the U152 expansion was still happening reasonably late in history, during the Middle Ages, and it was not mainly completed by the time of the Italic migrations and later the Roman expansion? I concluded something like that based on your assertion that part of the genetic differentiation between the two regions as far as U152 is concerned may be partly attributed to the relative and reciprocal isolation for much of the Middle Ages and Modern Era. Your point about how the southern population is much more similar to one another than the northern population, which has signs of more genetic isolation and drift, is very interesting, indeed.
3) I was maybe a bit too enthusiastic and hasty to assume that R1a(x M458) means necessarily R1a-Z93. It may also include or even be mostly composed of R1a-Z283 clades except for the "typical Slavic" M458, and still a brother of R1a-Z93. R1a-Z282 (x Z93) seems to be much more common in Greece than Z93 alone, though much of it may have come with Slavic (and maybe some Turkic/Avar too) input. But I still think that the heavy frequency of R1a (x M458) in the South Italian samples of that study may also suggest to us that the Ancient Greeks already had some of that non-M458 R1a in their original gene pool, not just the often speculated R1b-Z2103, J2a and J2b.
1. I completely agree. I used to recount that Portuguese sometimes sounded to me a bit like the Ligurian dialect, and that's why I found it relatively easy to pick up.
I don't know. Maybe that was my imagination.
2. Until we have the ancient dna it's difficult to estimate how much U-152 might have made it into the deep south in the Bronze Age, let's say. Could it have been very much an elite migration? Or, was there a more significant amount which might have been diluted by the Greek migrations as well as the Iran Neo "like" migrations which also came in the Bronze Age? Any subsequent migrations also have to be considered, even if it's only a few percent.. Even with ancient dna it may be difficult to come to firm conclusions.
All I was getting at is that other than the "Lombard" migrations into Sicily, you didn't get much movement of more "northern" clades into the south after the Roman Era. There also was no movement south to north. The south, including Sicily, was either part of the Byzantine Empire, or the Normans, or later the Spanish. Whoever ruled it, it was largely one unit, which permitted internal migration but inhibited migration to or from the north.
As I said, the Lombards used to pacify the island after the Moorish control of about 200 years is another story.
https://en.wikipedia.org/wiki/Lombards_of_Sicily
I've met Sicilians here who have ancestors whom they've traced back to my own Liguria and Emilia in the Middle Ages, very high U-152 areas. They came from Piemonte and French areas like Brittany and Normandy as well, although that would have brought a different pattern of yDna.
One of the things which has always struck me about Italian genetics is indeed that southerners are pretty similar to one another. Northerners are more different from one another from what I can see, as well as obviously different from southerners. Part of that is different migration waves, the Apennines which separate west from east, but part of it is also that for most of the time we were separated into different kingdoms, city-states etc.
Just a small personal example: in all the time I've been on 23andme, all my close legitimate "matches" are from northwest Italy and Tuscany, none from Lazio south, but also none from Venezia or even eastern Lombardia, Marche, or even Romagna. It's amazing.
3.) I don't know what R1a (non M-458) the Mycenaeans might have carried, if indeed they carried an R1a lineage rather than the often cited R1b one, but whatever one it might be, there's very little of it in Greece.