Miku development is mostly about her gaining more self-esteem, at the beginning she was unable to be honest with her sisters about what things she liked, she thought of herself as the one most likely to fail and how there was nothing special about her because her sisters could do everything she can
now she's pretty open with her sisters about liking Fuu and thought of herself as being good enough to get the top score at the test, she even tried to beat Nino at cooking even knowing it was nino's specialty
she's still has some more development to go through, like finding what she's specially good at and stop using fake directness/disinterest as a deflection (this one may have been done after last arc but there hasn't been a good moment that shows this development yet)
compare that with nino's development:
went from "i don't like this guy" to "i like this guy, i just didn't like he was only helping us only as a job"