Tbh, it depends a lot what other mechanics the sisters have, and how many unique effects the super equipment will give. I think throt "only" gets the flesh lab, whereas sisters in theory get various unique events and storyline missions (and more/greater access to the moth lady).
I find the whole dichotomy a bit weird though... they come in the same dlc, so why is anyone upset? You have to buy both. I guess people are bored of playing skaven, but then shouldn't they be glad they make bigger changes to skaven so there's more novelty?