I felt the characters were sufficiently developed for their various purposes within the movie. We spend as much time with them as we do LUKE/LEIA/HAN in ANH.
What exactly do we learn about Chirrut Îmwe, Baze and Bodhi Rook other than the templates for their characters? Not much…Can’t say the same for Luke, Han, Leia, Rey, Finn and Kylo Ren.
What do we learn about Chewbacca and R2D2 in ANH? We don’t need to have some sort of comprehensive emotional arc for each character necessarily.
In the case of Baze and Chirrut, I found the theme of renewed faith quite resounding - especially as they live in a universe where the Jedi have just gone extinct. Bodhi is constantly terrified - but then does something brave and feels fulfilled - almost like a watered down Han I guess (selfish - selfless).
As someone said earlier, the film is really about the Empire and the Rebellion, where as the within the OT they are just merely components of the larger story.