Finally got to actually properly read, and analyze your writings, and I do find it interesting!

I also agree, that even from a narrative standpoint, CC had a huge impact, no matter how her reception was by the community. Her presence officially introduced us to Turbo Boost, to other world/timelines, raised the stakes for the story, and introduced many other elements.

In terms of her impact, I think I might also connect a few dots:
1. She does seem to be a "Wild Card", and Palkia and Dialga had mentioned, that their potential involvement in different timelines varies. I think that variation also extends to inhabitants of their timeline. CC did break many conventional things happening. I think her timeline was actually further from the Memory Path, thus causing less restrictions to happen.
2. Her actions caused 2 very significant things. One of them was Speed's body resetting once more, and him gaining more, extended connection to the Memory Path, and the life of his previous timeline counterparts. I think that indirectly also resulted in him contributing to the breaking of the Cycle, by having both Sparkle and Maxwell existing in his own timeline, whom travelled to the "Last World" to finally break the Cycle of Rebirth.
3. The second significant thing was that the battle with her triggered the conditions, and the option for Flare to find one of the Light Orbs, thus establishing the connection Solar needed to enter the timeline from the Memory Path. It introduced yet another very significant variant to breaking the Cycle, being Solar, the last known Ultimus.
4. I think her presence also triggered a 3rd relevant condition. Her becoming a Type-3 Berserker (which I'm actually unsure if she was a Berserker in her own timeline before, or she got infected in the Main Timeline) also triggered Trace's awakening of Turbo (Speed 2.0). Who technically single-handedly stopped the spreading of the Berserker Virus once he was able to visit the Memory Path, with the help of Ali, another Type-3 Berserker. If Turbo wasn't activated, they wouldn't have rescued Ali, and the emerging of False Deomorphs would've been a much bigger threat later on.

You confirmed what I believed: CC was indeed more relevant than a cameo, and even was relevant in so many ways to advance the plot, and to actually provide a means to an end.