Doesn't matter; the I2a men didn't need to recolonize via Ukraine; they waited out the LGM in the Bosnian refuge; and I would like to see sources indicating heavy R1a movement into Europe back/before/during the R1b/ I days of moving into Europe. (I men arrived earliest).
I can agree with you that probably I carriers were first in the Balkans, maybe 25,000 years ago, maybe earlier. But they moved.
R1a carriers came to the Balkans about 10,000 ago or more? (scientists are dealing with large differences dating back Balkanic R1a in Paleolitic or early Halocene). It is mistake that for these first Balkans R1a carriers some members of forums think that they are Slavs.
R1a carriers massively came to the Balkans about 3000 years BC and after. And it is for debate whether they are Slavs. These R1a carriers are associated with Indo European Kurgan culture.
Naive observers think R1a=Slavs and R1a came to the Balkans only in seventh century. No. In the world there are a lot of R1a carriers who are not Slavs. And today's Slavic people are mixed R1a/I2a but and another haplogroups.
R1a is very old in the Balkans and scientists proved this. But some observer can notice that R1a is quitle evenly distributed among today's Balkan's people: Serbs, Greeks, Bulgarians, Albanians, Bosniacs, Romanians, etc. Somewhat higher in Croats and even greater in Slovenes (but Slovenes are not in the Balkans).
For example difference between Serbs/Bosniacs/Croats and Albanians is not so R1a. All people have R1a in some significant percent, including Albanians.
Main difference is I2a, because (Geg) Albanians have small percent I2a. Tosk Albanians have much more than Geges. Eupedia don't give right picture (you can see Albania, Kosovo, Macedonia) because in Albania there are no division Geges, Tosks, and in Macedonia there are no division Albanians, Macedonians. Kosovo is more realistic because Kosovo Albanians are Geges (there are no significant numbers of Tosks in Kosovo).