>another V6 or nothing doll
Why is this allowed?

In case you're wondering, Qiuhua's core mechanic is called Scorch Mark, which builds stacks when burn DMG is inflicted to the target afflicted with that status and detonates at the end of the turn, resetting the stack count (at V1+, her ult detonates the stacks while not resetting the count, so it happens twice per turn). At V6, the cap is removed (the normal cap is 12) and her damage output becomes the highest in the current version of the game. However, Klukai and Springfield are still better in terms of account value because they're way more flexible and can be put in the most diverse teams while Qiuhua is exclusively mono burn.