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.
Why do people insist on asking questions like this?
What do you learn about Luke Skywalker?
Not much but you go on a journey with him that is about it and he has 3 films as the main character. If you were expecting a historical epic about someone you will not find it in Star Wars films.
Go and watch Ben-Hur or something?