Not to say that Leia doesn't have skills in addition to diplomacy: In the fight during the jail breakout, she showed that she was able enough using a blaster, was athletic, and showed ranks in Command. It's just that during the space fight, none of these skills seemed relevant. One could suppose she provided encouragement to the others, but that doesn't seem to quite be active enough of a skill use.
Yeah, characters on screen don't get bored when they don't have an active role in the current scene!
