No need for it to be fleshed out in the movie wouldve made it even longer. If anyone shouldve been fleshed out a tad more would be the characters just to help make their motivations to back each other and call Jyn their little sister make more sense. Saw's role was fine. He took care of Jyn for her parents. Developed her into an elite soldier at an early age. Left her on her own to keep her safe and more importantly even more hidden. Thats all we needed.

Def wouldve been awesome to explore it more and really see their relationship but if we had to choose between him and the "main" characters I choose the main characters.