That's why many automatically assumed their powers awakened during the fight; that is also the reason why we're seeing a lot of people, especially Luffy fans, complaining about their powers being asspulls. It also kinda goes in line with them not trying these abilities atop the roof. I know people don't always use all of their abilities, but it worth noting that this does indeed go in line with their rooftop battle.
I don't see the issue with the rooftop to be honest. Zoro himself only used Asura as a last ressort against Kaido. He didn't use it against hakai, and he only used Asura as a desperate move to save his captain especially since he was getting too weakened to be of use after the hakai
To me, it's just that Oda decided to use Zoro in that particular instance since it was his highlight moment before facing King later, when he was reserving Kid and Law's highlights moments against BM
As for Luffy, as we all know with Oda, he always reserves the best for the last. Pretty certain Luffy will show awakening himself during the battle against Kaido. It's just that unlike a planer like Law(who already knew they were going to face a yonko), Luffy develop these kind of things mid battle on the fly