Rogue One isn’t a movie about characters, it is a movie about the state of the galaxy and how that affects the characters living in it, and to that end, I feel like the characters were kinda meant to blend into the backdrop a bit, because the real characters of the film are the Rebellion and the Empire. It’s just not a character film, and I don’t think it was meant to be one.
I don’t feel like the character writing was especially weak: was Han any more developed at the end of Star Wars than Cassian? Ignore Empire and Jedi and Awakens. Leaving the theater, I felt like I knew each character’s archetype and story as much as I do at the end of Star Wars. And I felt the story writing was very strong and all worked and made sense.
I’m going to have to get back to you on this one…