Lol, Zoro is pretty far from going all out. Leaving aside Asura, he hasn't even used Hardening or his upper tier Santoryu techniques yet.
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Law and Luffy are the SN who have been shown the most in the time skip, we knew quite well their attacks and potential (at least until pre-Onigashima raid), we can make hypothesis based on what they have shown before and what they're showing now.
We haven't seen much of Zoro and anything of Kids and Killer but that doesn't change the logic of my argument, unless you think that the 3 Supernova or just Zoro didn't use CoA against Kaido (What's the motivation? Why attacking the strongest of the world without Haki?) or that 3 sword style is more powerful than Luffy's most powerful techniques (Luffy is the strongest in the crew and on the roof, his best attacks should be stronger than Zoro's best attacks, Ashura, maybe by a little).
Just supposing, tell me what's your opinion.
But, anyway, the point doesn't change and is "Supernova need to inflict more damage than that given by Gear 4th and Gamma Knife" and it's like saying "they must have something more powerful than their already known first-second tier techniques, if they want to beat Kaido"