I haven't read TPOTS yet, but I didn't mind the spoiler. Like the reviewer, I have a strong dislike of using the rape trope to move the plot along, when there's no reason or real justification to have it happen. Just to set up a Big Bad is neither a reason nor a justification. And that's why I think you got it right. Rape isn't used to prove that Ferris is a bad guy; he's a bad guy who acts in character, and for him that includes the rape.