The way I see it, the Tantive IV and Leia were shoehorned into the movie as per Disney’s demands.
It would have made a lot more sense if the ship escaping from the Battle of Scarif wasn’t the Tantive IV.
It definitely seems like many of the continuity issues at the end of the film were a result of reshoots (the late addition of the Vader hallway scene comes to mind). I’d very much like to see a director’s cut and how the ending was meant to go originally.
I remember reading that originally Gareth Edwards intended for the movie to end with Jyn and Cassian being killed by Vader, but this ending was deemed too dark.