Lights out stip was needed, because they need an excuse for this to go last after the World title match. I could be wrong, but I don't think they have ever had a World title match not close the show.
There is also the factor that Hangman needs to win this one, and they can use the gimmick that he never beat Swerve in an "officially recognized" match to feed into another match down the line when it's time to revisit it.
The story they are telling with Hangman, about whether he is a soft dad, or whether he has that killer instinct. It's a chance for them to push things further and turn him into a legitimate dangerous top heel. If Bryan can't go long-term with the belt, he should be the one to beat Bryan, and he should absolutely murder him.