Is that why Luffy needed Zoro to protect and save him? Is that why Luffy attacks caused Kaido less damaged than Zoro's? Is that why Luffy couldn't do anything against hakai.
Work on your reading comprehension skills. Kaido asked himself that question because of how quickly Luffy was able to obtain the power damage him. Luffy couldn't do anything to Kaido of the last time they fought.
Kaido didn't ask that question about Zoro because Zoro already had the power damage Kaido they first time they fought so Kaido had nothing to compare Zoro's previous strength to.
Zoro recreated Oden's legendary scarring Kaido feat on the rooftop. That the same Oden that Kaido wondered if Luffy could reach his level. Kaido acknowledged Zoro's strength.
Once again, Red Roc dropped Kaido and had him acknowledging Luffy's strength in a way he didn't do for anyone else. Kong Gatling also had Kaido on the ground for a while whereas he brushed off Tatsumaki pretty quickly in contrast. Zoro's scarring of Kaido was so inferior to Oden's, Kaido stayed standing, told Zoro "you did enough" and KO'd him immediately after. Oden still gave Kaido PTSD 20 years later in comparison, never mind his scar clearly being a lot bigger too. Kaido didn't spare a single thought for Zoro after the second scarring.
Why do you assume Luffy couldn't do anything against Hakai just because Zoro got ahead of him to take action first? You're telling me to work on my reading comprehension while insinuating Luffy wouldn't be able to do what his subordinate could? And Zoro would've died in seconds had it not been for Law teleporting him out anyway.
Finally, learn the difference between blunt attacks and cutting attacks. How is Luffy going to leave a scar with his fist? This is all before Luffy rocked Kaido's shit with unrefined ACoC in Chapter 1010 btw, putting Zoro to shame with that final display.
Zorotards like you are completely hopeless though, you're the type to think he could've handled Doflamingo because he apparently didn't grow in strength from FMI to Wano Act 1.