T'was me who said 90%!
She is a more powerful package that Arjuna Alter overall because her neutral damage is similar but she is significantly more survivable; has pmod on her attribute advantage, pmod on 1 of her class advantages; and a wide traitmod.
So for a large amount of enemies she outdamages him on NP quite substantially. For a smaller roster she outdamages him on face cards. All whilst bearing the strongest defence on a proper Buster attacker and 10 passive stars/3% NP per turn.
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She is far stronger than Melusine in AoE mode, with the caveat that Melusine can brain dead farm chargeless and Kuku cannot. Her neutral is way above Melusine in both cards and NP and she has traitmod/pmod to push further.
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Unlike Morgan she doesn't enable a stall shell, her resilience is selfish. So we basically have a package here that is "generally better Arjuna Alter", able to cleave 90++ earth/threat/advantage aoe check waves with just KoyanDark providing NP, and able to monoDPSteam nuke in the 600-700k* range at neutral with an event gauge starter.
*fully maxed
And this is on her huge body with a BBB deck and always enough stars to crit.
However...
I think S.Ibuki is probably a more reliable farmer on the off chance we get more chargeless events, although Kuku's mods and stats are high enough she can function as a 2nd attacker with investment.
Likewise Melusine will be useable on Archer/Berserker chargeless 90++, where Kuku would need to drop a slot (or punch a 1 enemy wave) and for an 800k non-Earth Archer, face punch once.
So overall she is definitely powercreep within Buster but not where chargeless farming is concerned (which screws all but Arc/Melu, and Arc lacks damage for 90++ without 200pmod CE kr BG+Chaotic).
Her value in a multi-DPS team is similar to Morgan (charisma+stars, own big traitmod NP) but minus split battery.
And compared to the previous Buster AoE Foreigner with Earth traitmod, Kuku does 1.5-2x their damage at neutral. Her neutral outdamages their traitmod even with OC up!
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ON QUICK:
Quick's core problem has never been damage relative to Arts. It's a total lack of consistency and teambuilding tools for farming, and absolutely 0 ability to extend within colour.
Higher end Buster is absolutely outdamaging NPAB from Quick though, even with S.Skadi's bigger crit buff. And NPAB chains are not a reliable attack choice for the numerous QQAA Servants they've released since Voyager.