Reading some of thoughts of the readers here, I think Miku did really taking into consideration all the things that happened in this arc. While people viewed Miku brushing off her confession as a negative, I think it was very smart of her. Fuutarou just isn't ready to confront these feelings. Miku getting Fuutarou to kinda say it and be more aware of it while having her confession saved for a better time, it's the best case. Not to mention, I don't think it would be that meaningful to her as well as she received a lot of help from her sisters.
Regarding Nino, I always think that her personality can work against her. I always thought that her confession was of poor timing. The mood was not set to have any meaningful impact. From here on, I like forward her advancement goes.