knights's core concept is heavy on fanservice, based on a character role (knights), and appeals to princesses. esupuri's core concept also is heavy on fanservice, based on a character role (princes), and appeals to princesses! you can see the similarities in how they both have special nicknames for their fans, etc. i think that's the main reason surrounding the complaints.

fine in contrast has no core concept shared, just i guess sort of a light color/pure white theme. they are actually not princes, but are more akin to angels (as they handed out divine punishment in yumenosaki). tori sometimes is given princely theming, though. but fine is mostly characterized by their elegant style.