That said, this is a point of contention that even the authors of the paper allude to:
"The most principled approach is thus to build ancestry models in which source and ‘outgroup/reference’ populations are older than, or at least contemporary with, the target genome or group that we are trying to model. However, this has been challenging, due to the limited statistical power offered by the thousands-fold lower sample sizes and reduced sequence quality of ancient genomes"
Iron age British ancestry being found in Ukraine with Viking graves also sounds really fascinating.
But frankly, this paper is not about captured females(which btw are more uniformly spread across whole Europe, so their capture even in Southern Europe would not radically add anything new to a Scandinavian female gene pool), when it specifically mentions whole populations coming to Scandinavia from Central Europe. It is differences in males that really make distinctive population groups.