I think kishi made Karin the mother so he could make drama and drive the theme of genetics don't make family.Y would Karin leave Orochimaru's hideout after all this time :|
Kishi may have trolled, but it was definitely with a purpose and therefore necessary to the plot. With that being the case I don't think going back on it is an issue since the troll actually solve problems
Also in the case of BZ and Maddy it had a goal which was shifting the villain. Having Karin be the mother changes nothing