Yup, Acy is right about the cooperative angle. It certainly strikes me as unfair to some extent that the highest scoring players would be "penalized" by having their characters and everything they worked for throughout the game taken away from them and instead they are forced to play as someone else [Lucifer].
I think the only way this would work is if there were an Opt-In system where players get asked at Wave 16 if they would want to be Lucifer. And that only exacerbates some of issues I listed before.