Luffy hasn't used G5 better, he's used G4 better, and we have no idea if the drawback is entirely removed or how it actually compares to a full G4 transformation.
AP is one attribute, Kaido was also outperforming G5 repeatedly.
He was called the strongest by Kidd/Killer and King who aren't fodder, Oda in an SBS, many times by the narrator, in the databooks/vivre cards, Ace novel, and Kaido himself says he's the strongest after fighting Shanks, and obviously knowing about the strongest people alive at that time.
Luffy has not surpassed Kaido at all.
Kaido > Shanks/Dragon/Akainu/current Blackbeard is already stated, only one of them has been called the strongest alive.
Your opinion doesn't overwrite things stated within the manga and even by the author himself unfortunately.
In the end feats are important for me, Statements been said and only implied that Kaido was be said to be the strongest.
In fact we never hear a statement with said "Kaido is the strongest" but was said to be the strongest. Killer only repeat that line, Kid never called him the strongest.
And that is the point, Killer never saw someone like Kaido, since they never saw Shanks in first place. Oda tricked the community knowing it would hype people with Statements like"said to be the strongest". But he doesn't needed to confirm it, since in his mind he already have character in back up who gonna surpass Kaido.
We saw only two top tiers fight with Kaido, one vs Oden and the another vs Luffy.
And Luffy surpassed Kaido, G5 could toe toe against Kaido, yes he still Dominated him, but he couldn't knock out G5 anymore, he used all his strongest attacks and failed to put down Luffy. That is the point, G5 is above Kaido, since G5 can knock out Kaido(seen) but Kaido can't knock out G5.
Everyone can try to stall G5, but if someone can knock out G5, he show to have stronger AP than Kaido.
And that is the point.
Current Luffy is high diffing his EoW Luffy Version. We saw Luffy can now use G5 without transformig into a old men if he use it for short time. We saw him using now G4 far better.
Law can now use his awakening very casual, got haki boost after his battle against Big Mom.
Means they get stronger.
Luffy just needed two weeks and a extrem battle against Kaido, to jump from high high tier(Kata lvl) to mid/high top tier lvl(Kaido).
And you know how much time pass after his battle against Kaido was now one month(even longer) ago. Means he had 4-6 weeks to even grow more stronger. And before you coming up with stuff like he didn't had hard battles, he had a full battle day against Lucci,Kizaru and Gorosei.
Current Luffy got stronger.
He can easily high diff his EoW Luffy.
He is Kaido Level.
And if Loki can fight current Luffy equal, he is equal to Kaido.
Shonen manga never introduce one of the strongest characters few arcs early. They always show up one/two arcs before the final villian of the manga shows up.