Indeed, Danubian Tumulus culture and Urnfield groups were packed with R-L2, and the La Tene Celts brought even more of it. We know they lived along the Danube, side by side with Illyrians and Daco-Thracians before the Romans came.
As for E-V13 and Balkan Iron Age profile, its clear we're dealing with different groups (South Thracians, North Thracians-Dacians, Illyrians etc.) which were however, autosomally, all not THAT FAR from each other, especially in comparison to the incoming Anatolians, Germanics, Iranians, Huns-Avars and Slavs. Therefore relatively speaking, they are almost a unified block, and the main difference will turn out to be patrilineages anyway (Illyrian J-L283 vs. Thracian E-V13).
It's the same in the West, with the difference between Germanics and North Celtic tribes. Those are much harder to distinguish, especially in transitional zones, than they are to differentiate from outsiders. And this "local" (to the macro-region) vs. "foreigners" (to the macro-region) is what this Balkan Iron Age profile or genetic range is about. Its not more than that.
Obviously if digging deeper, especially with uniparentals, but also autosomal admixture and IBD analyses, more could be told about the differentiations within the Carpatho-Balkan sphere. Because this "Balkan IA" genetic legacy won't be restricted to the Balkans, but extend far along the Danube and up to the North and East Carpathian sphere, basically where the Daco-Thracian/Thracian Hallstatt populations had their homes and colonies. As well as to Italia, where Illyrians landed etc.