C6 Meta power

Looking at the stellar calcs done by theorycrafters, i see that they calcs a lot with qiqi at most at c2, and i do not think i 've seen any calcs with her at c6. Is it because even at c6, using her burst is not worth it for the best meta teams or because they just assume cost investments?

As such, at c2 levels, in those calcs she is never quite BiS for any team, a sidegrade at most. But is there any context where she would be BiS for anyone at c6?

If it's just that i'm blind and did not see the right calcs then sorry and thank you for your time