You're misunderstanding Shiho's character flaw. It's not like Shiho runs away from adversity out of angst. Her character flaw is her inability to except she's not number one, and the fact she keeps antagonizing Aki and Yori proves she hasn't changed.
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.
On a mostly unrelated note Hima could use with some character development herself so she stops agreeing to ridiculous demands. Her immediately agreeing to be their band manager for life was very cringe worthy after all the trouble her original agreement caused her. Luckily it was a joke since I'm not entirely sure that Hima wouldn't have followed through on her agreement if pressed.