As some other scientists, I also see paleo-Balkan people as direct ancestors of Slavs.
So, it’s not unusual for South Slavs to have most Ia2a haplogroup (provisionally named “dinaric haplogroup”, it is hypothesized that this haplogroup spread from the Balkans to the areas of central, eastern and southern Europe prior to the Early Neolithic), while Albanians (ethnic mix) to be most of E3b and J etc. haplogroup.

“The first occurrence of haplogroup R1a in the Balkans are located after the last ice age maximum.
In addition, leaving the possibility of further inflows in the period 3000 – 2000. BC, as well during the so-called “Migration of Slavs”, but the latest variant of the least credible, given the general population trend of continuity and unreality of mass migration.”
Dr Nikola Dimitrijevic

It is also very interesting that highest frequency of hp I2a2 is in Hercegivina, were according to historins lived “real Illyrians” (“Illyri proprie dicti”).