This is exactly the kind of information which you can't glean from rankings.
The quiz sets up a highly emotionally charged situation that a lot of people are going to make snap judgments about. The first couple of ranking decisions made are going to reflect those snap judgments. The neat thing about the ranking process is that it forces you to think beyond the snap judgments and consider the relative morality of all the characters. It asks you to do this while your guard is down, i.e. if they just asked you the relevant questions about your moral leanings, you wouldn't necessarily give the ones you are really operating on subconsciously.
The other neat thing is the ambiguity of the situation given. You don't know the character's histories, you don't know why the sheriff locked them up, the whole thing is set up so you read those details into the situation. What you read into it will certainly affect your rankings. For example, an unassuming reader won't snap to the judgment that the sheriff forced Maid Marion to have sex with her.
Your proposed swap is really weird, placing Little John above Robin Hood but Robin Hood above Maid Marion. It indicates that you accepted that Little John is the real mensch in this situation, yet identify with Robin Hood's caddish behavior anyway.
The real decision here is whether Robin Hood is more honorable than the Sheriff. Ultimately the Sheriff was more honest to his baser desires, whereas Robin became irrationally controlling when confronted with a difficult situation.
If you thought Little John should have gotten the prize, then to be consistent, you have to put Robin in the loser's spot. Robin Hood chose wrongly when confronted with a moral dilemma in a way that traumatized the very person responsible for his freedom.
Giving Robin more credit than he deserves indicates that you identify with the feelings he had. They're the feelings of sexual inadequacy and possessiveness.