You are right. But imagine if there was an opportunity to influence some of the daughters, for example the way Olivia can with Elena (under certain conditions). I think it would be interesting to give the players a chance to try and change them. Yes, I know that the author is sticking to her own plan for the future development of the game. And if those plans only spell out the possibility of Olivia influencing Elena, then it's hardly worth waiting for something similar in the MC's relationship with Alexander's daughters.
One could say that the Olivia<-->Elena case is special and there is a deep mother-daughter bond, so such influence is possible, whereas in the case of Kane/Olivia<-->Alexander's daughters there is no such bond and therefore no prerequisite. Fair enough, but the author wrote that in addition to femdom/kinks, she also likes romance in relationships, so a hypothetical love route with either daughter (except perhaps Juliette) could conceivably be a prerequisite for the daughters to change (e.g. near the end of the game). And it could have been one of several endings, or part of one of the endings. (Yes, Gambit first, but still...)