I think Slavic is more like R1a1a7, most likely I2a2 was slavonized and goes hand in hand with R1a1a7 for good 2000-3000 thousand years. But I wouldn't bet on it maybe it was vise versa. I'm not sure if we can call R1a Slavic in general, more like protoslavic, but about 4000 years ago it was same as protobaltic. Maybe we should call it Scythian, most likely they gave rise to Slavic, Baltic, Iranian, Arians before the split. Before that 5000 years ago, R1a Battle Axe culture dominated central, east and North Europe. Genetic record show it was the first incursion into central and north Europe. I think that's the time they started mingling with I2a2.
I'm really looking forward to extensive genetic testing of old graves from this region to really shine light on the subject. Bustards didn't leave us any written word, lol.
PS. Did you came upon info about who were Venedi?
PS. There was a legend in Poland that the ruling class came from Sarmatia.
I was looking at maps showing Sarmatea and Scythea, they all show something different lol, hard to trust one.