The director has mentioned that Evolution was used because it was the quintessential "Shibuya"song. Also because Ayumi at the time was losing popularity as Ririco is in the film. Interview is here @7:55:
Also, I kind of think Erika referenced Ayumi at the opening day press event. She never appeared with this hair style again and it was the one Ayumi wore around that time and the one Ayu was in when they were together at an event.
Lol
Helter Skelter is definitely its own thing (The manga was made before Ayu's debut), but the film obviously drew parrarels to Ayu as she was the quintessential pop figure to the Japanese public that an audience would relate to. Just like how Natalie Portman's character in Vox Lux (which btw makes a great double feature with Helter Skelter!) has a bit of Gaga, Britney, Madonna, etc.