One Red Roc had Kaido dropping his top 5 and wondering if Luffy could reach those heights, when did Zoro make Kaido shook like that on the roof? Rooftop Luffy would still convincingly beat Rooftop Zoro in a 1v1, not a low-diff though
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.