The people were sleeping on Luffy for a long time since he got one-shotted by Kaido.
Luffy is the
Fifth Yonko. He is the strongest one there, and everyone was waiting for Luffy and not doing anything until he arrived.
Blackbeard said it was still too soon for Luffy to be the Fifth Yonko, but now he has completed his Advance CoA Training, we can safely say that this Luffy deserves to be the Fifth Yonko right now.
We all know what will happen, everyone will put up a good effort, but Luffy will be the one last man standing. Just like it happened in Doflamingo fight. We've clearly seen Luffy > Law, now we will see the similar thing, although the rest is debatable.
Why Kidd is above of Law? While Law's DF power is extremely powerful, and it's very useful for team fights, Kidd has one advantage here and it was foreshadowed since the beginning of Wano arc;
Doflamingo put Luffy over Law, based on CoC Haki. And was he right? Definitely, in the end Luffy performed better when it mattered. Doflamingo and Luffy stood above Law, they were two CoC Haki users. Then Katakuri with CoC Haki. So now, E.Oda will give even a better opponent than Law for Luffy, it will be Kidd with CoC Haki. Obviously it's Kaido > Katakuri > Doflamingo, however I am talking about friendly competition, like Luffy and Law had, now that we know Luffy with CoC Haki is above Law, we need to learn how he surpasses Kidd in the fight, who also have CoC Haki like Luffy has.
E.Oda already showed us that Luffy and Kidd were competing all the time, not only they have the same CoC Haki.
I believe this time it will be like Luffy > Kidd > Law > Zoro > Killer.
As for who will kill Kaido? I believe Big mom is there for some reason, and we don't know who exactly betrayed the first Rocks which was the reason why they failed. If it was Big mom, then she will do it again, and betray Kaido. If it was Kaido, then Big mom can always say you betrayed Rocks, and now I betray you, so she delivers the finishing blow, kills Kaido and leaves Wano after getting defeated by Luffy, Kidd and Law alliance.
I believe Big mom's soul ripping power is perfect for delivering the finishing blow to Kaido. And we also know the marines won't come to the Wano, so Kaido needs to die, X-Drake can arrest him, but I don't think it's time for X-Drake to reveal his true identity yet, and the Wano's borders still not opened, so the marines shouldn't enter yet. No doubt that Zoro will cause damage to Kaido, but there is no way he will outshine Luffy, not even Kidd or Law in my opinion, so I expect from Big mom to betray Kaido once she realizes that they will lose against Luffy, Kidd and Law alliance, and kill Kaido with her soul ripping powers. Which is also a good narrative that she is responsible for Kaido's power growth and fall of Wano by giving Kaido a mythical zoan DF power, which is rarer than even logia and she will be the one to end Kaido's story, we can even see their flashbacks from their Rocks days.