You don't necessarily grow stronger against a weaker opponent. The only difference between rooftop Zoro vs KoH Zoro is his ability to draw from Acoc at will as opposed to by luck. Also the version of Zoro that used Asura on Kaido and the version that fought King had the exact same mind set. To release all his power without restraint. They're essentially the same thing.
Acoc wasn't the only thing Luffy needed to beat Kaido. Otherwise the fight would have ended right after Luffy learnt the technique.
He went through multiple power ups including gaining mastery over his conqueror coating until he could match Kaido completely. Even before the fight Luffy had FS which Zoro does not have. Kaido also had it too along with a bunch of other things he had held back until Luffy forced him to get serious.
Zoro is lucky he never had to deal with Thunder Bagua or any of Kaido's signature attacks apart from his aoe attack. He's also never fought someone who has used Acoc. So he's behind on a number of things.
Zoro don't have to face an opponent stronger than him to grow stronger. Not all of Zoro's previous opponents were stronger than him. Zoro can grow stronger from fighting weaker opponents as long has they provide him an obstacle he must overcome or show him a weakness he must remove.
Braham wasn't stronger than Zoro. Yet, Zoro grew stronger from their battle. Zoro obtained flying slashes from their battle.
There's a huge difference between rooftop Zoro and KoH Zoro. Zoro had two major growths during Wano war just like Luffy. Zoro obtained ACoC and Enma mastery. While Luffy obtained ACoC and awakening. The main reason Kaido acknowledged Luffy's strength and saw him as a worthy opponent was because of ACoC, not his awakening. Just like Luffy, Zoro gained mastery over ACoC.
Even FS was pretty useless against Kaido. It barely tickled him. Only the trajectory of Luffy's Snakeman attacks was troublesome. Luffy won because of the strength of his attack.
KoH isn't just ACoC. It's ACoC combined with overwhelming amounts of CoA haki. It was because Zoro learned to fully control enma he was able he obtained the power to release and control larger and stronger amounts of CoA haki. Stronger/larger haki equals to stronger offensive and defensive power. Zoro's haki power on the rooftop was strong and troublesome against 2 Yonkos.
Zoro mindset changed against King. Zoro acknowledged he couldn't full control enma because of his own weakness. He remembered his promise to his best friend and captain to become the WSS and stopped worrying about using up too much haki with enma. That was when truly awaken him CoC and King saw him as a King (King of conqueror).
Kaido attacked Zoro with TB and it failed to knock Zoro out even though he was already in poor condition with 20 to 30 broken bones.
What about those other things Kaido has? You don't seem to understand KoH is not rooftop Zoro who already have the power to block hakai and scar Kaido in a poor condition. This is a Zoro who mastered a sword only Oden could master. Who obtained the exact same power that Oden used to scar Kaido, almost 2 shot, and place him on the same pedestal as Roger, WB and more. Who has grown stronger since Wano. We still haven't seen how powerful Zoro's high end attacks are with KoH or dragon style.