Responses
The MC didn't become heroine. If I understand correctly, there is no heroine, just two villainesses. They said "become the complete darkness to bring downfall to a more dazzling villainess" so they both are villainesses . Also, I think Seori could have resisted the system if she was aware they all are in a kdrama like the MC
So the settings finally changed and Han Seori became a villian, it kind of sucks it went that route because I wanted to see MC fight the system not become the "heroine"... if that makes sense. Also I wanted to see Seori also break the system that pushed her to that role because again, she was about to reflect but was "corrected".