the difference being is that the slavic peoples solidified outside of europe unlike the rest and didn't migrate in until the beginning of the fall of rome and the pressure from the central asian hunnic peoples in the dark ages, other groups came in 3-4 thousand years prior if not more.So did half the groups of the migration period that ended up in Europe. The only reason to specify Slavs as "Asian" is to arbitrarily exclude them from Europe. Ethnobrained writers in Europe have been doing this since the 1700s.
You know what Indo-European is right?