Agreed but for luffy it's Awakening. From doing nothing or barely managing kaidou ,he went to dominate kaidou with g5.
For Zoro it's understandable given his mode of power up is only limited to Haki , which is why he rocks stronger than Luffy.
Luffy Without G5 would have died in front of kaidou without doing anything major. And note this One had AdCoC.
You say he was doing nothing or barely managing Kaido but he was hurting him really badly even in base with ACoC, when he went G4 he was aknowledged by Kaido and their fight was called a world class battle by the Gorosei, this is what I mean bro. He went from scrub to top tier with ACoC. Its a huge boost. G5 was needed to get him even further because Kaido is that much more of a monster that even if you become a solid top tier you still need more to beat him even while hes weakened and nerfed.
The fact that Luffy needed G5 to win isnt an argument against Luffys ACoC not being a huge boost, its a testament to Kaidos strength.
Both G5 and ACoC complete Luffy as a fighter, without one or the other hes not as strong.