I think I prefer this way, the novel made no sense after the author has no more influence it makes no sense for the Duchess to not take action and Cliff and Reese to still get married.
i think it still makes sense tbh bc system or not, for the duchess and duke, they loved and raised reeze for a long time. it isn't so much like they're staying indifferent or 'not taking action' but more of them feeling betrayed by reeze and still thinking she's the same person they loved, and guilty for doubting edith time and time again that it renders them incapable of doing anything essential for the family. it makes sense this way because even killeon wanted out of the family that caused much of edith's suffering
The key word is “influence.” Meaning not total control but has the ability to have an affect on others. Like killian would sometimes be pushed to think a certain way due to the influence but would be able to make his own decisions regardless. The duke, duchess, and cliff were not fully under brainwashing like you think. They all spent time with her for years and still have that familiarity with her even without the influence.
I don't like how it's different from the novel but what we get is a nice couple at the end. + What a trustworthy guard that was assigned to reeze