Livy did make a few other conflicting statements. As I said, the main reason he may have considered them "Liburnians" was due to their geographic location: they weren't living in Gaul. As I stated before, the Vindelicians, without a doubt, were Celts. They were archaeologically part of the core Hallstatt area, and if you look at their tribal names and town names, there is also no doubt it that they were a Celtic people. But, let me take you through this with some examples:
Vindelici
Vindo- ("white"), compare Old Irish "Finn" and Welsh "Gwyn".
-licos ("rock", "slab"), compare Irish "Leac", Welsh "Llech", Breton "Lec'h"
Also take a look at the subtribes:
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Licates (also "rock", see above, also the Lech river - "Licca" in Latin, which would have been the "rocky river")
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Brigantes
"Briga" ("elevation", "climax" - also "castle") compare Irish "Brigh", Welsh "Brig".
There were also tribes of a similar name in Britain, Galicia and Ireland.
town names:
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Abodiacum ("Idle river")
"Abona" ("River"), compare Old Irish "Ab", Welsh "Afon"
"Diacus" ("idle", "dull"), compare Breton "Diegus"
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Artobriga ("bear castle")
"Artos" ("Bear"), compare Old Irish "Art", Welsh "Arth", Breton "Arzh"
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"Cambodunum" ("slope fort")
"Cambos" ("slope"), compare Irish "Céim", Welsh "Cam"
"Dunon" ("fort", "town"), compare Irish "Dún", Welsh "Dinas"
No offense, but you're making too many conjectures here, especially in regard for ad-hoc assigning certain Haplogroups to certain people. Haplogroup G2 is, as has been shown, Neolithic in age. It stands to reason that G2 had a roughly similar setup to today (that is, higher frequencies in mountainous areas) since the Chalcolithic. It is similar with J2. Both Haplogroups predate the ethnic groups in question by multiple millennia, so they are pretty unlikely to be of any help here.
Regarding R1b-U152, it was in my opinion already spread around by the Urnfield Culture. This means that the pattern we see today is the cummulative effect of Urnfield, Hallstatt and La-Tene. Specifically, I would think that the pre-Etruscan population of central-northern Italy, the northern Iberians in Catalonia and the people of the Lusatian Culture were all carriers of R1b-U152.
It would be interesting to have ancient DNA samples, yes, but that is generally the case. More smaples of
anything.