I don't see why she can't get low PCS even with a solid technical performance. PCS is not about technical skill but artistry. Furthermore, there should not be a fixed PCS point range for each skater based on their prior performances or reputation, because PCS is awarded based on the artistry a skater demonstrates in the actual performance itself, not based on the artistry they have demonstrated in the past. If a skater skates badly they deserve low PCS points. It does not matter if they have received an excellent PCS score in a prior competition. PCS should not be about reputation.
Also, the fact that the Japanese ladies got higher PCS points than So Youn is also not something that strange - maybe they simply skated with better artistry than So Youn on this occasion. Linking the points they received with their nationality is bad form IMO.