The real tragedy of this chapter is that it showed Shiho starting to grow out of this during her montage of Grave visits. She starts talking about not stressing over missed notes and having more fun and enjoying spending time with the band. She had decided to stop visiting the grave and living in Kyou's shadow. Then whatever it was between her and Aki happened and that all went away. She found out that Kyou thought her music was the best and started up her new band with everybody else who loved Kyou with the express purpose of being the best and living in the past.
So really there was a lot of character development in the chapter. It was just all erased in the same chapter. At least now we know that if Shiho isn't constantly reminded of Kyou she might eventually become a halfway decent person.
I agree with you. Many people couldn't understand why Shiho hates Aki and Yori just because she couldn't get Aki's love. Shiho got hurt by Kyou deeply in the past. When Shiho tried extremely to exceed Kyou, nobody agreed with her effort or told her to stop. If it were not for Aki gave her a hand, Shiho might be more distorted on that time.
Because of Aki, Shiho was starting to walk out Kyou's shadow. Finally Shiho can have more fun and enjoying spending time on band, she also fall in love with Aki. For Shiho, what makes her let go of the past is she expect her love will come true someday. However, Shiho found out Aki's love wasn't her. That just crush her belief and makes all the effort for walking out Kyou's shadow gone.
For a person who just get hope from a tragedy, the most cruel reality is that hope crumbled to dust, isn't it?