Scott was 3rd. She was probably 4th. Didn’t they call her Lt. Commander? Or was that in the movies?
No, Scott was technically not even bridge crew. As head of engineering if things are going poorly Scott’s not going to be on the bridge. Thus not high in the command structure. Kind of like McCoy, regardless of his rank McCoy will never sit the chair because if thing are that bad he’s got better things to do.
In the negative universe, Sulu took command. On the other hand, they did have the positive Uhura as I recall.
In the series, she was Lt. - not promoted until after the series.