>Developed her into an elite soldier at an early age.

Up above a bit I was struggling on why Saw needed to even be in this movie at all, but this is it. Him being there gave Jyn some depth in terms of how she would be able to take down stormtroopers with just a baton, and how she was able to lead a team of rebels into an imperial base to complete a mission. Without Saw, everyone would be wondering how this random girl who is the daughter of an engineer was able to be this elite soldier in battle all of a sudden.

If I could change anything about Saw, it would maybe be to not have Forrest Whitaker play him, but more of an unknown actor, and he wouldn't have been as prominent in the trailers. That's likely the reason why people feel he was underused and that he needed more character development. His character in the film did exactly what he needed to do.