Aching scar has way more significance than all you wrote
So does Oda repeating four times one must defeat the Yonko AND the Admirals to surpass Roger
Kaido's scar ached, yet he never faced Oden again to defeat him fair and square. And while Kaido thinks about Oden all the time, as Shanks thinks about Blackbeard, Luffy doesn't really waste a thought on Akainu.
Also, Luffy's greatest ability has repeatedly said to be able to make people his allies. And now especially as Joyboy, he is able to unite them all. Sabo in Dressrosa already took Luffy's place as Lucci, is said to have inherited Ace' will and, when finishing Burgess, pointing out how Ace still wants to exert justice on his enemies through the Mera Mera no Mi's power, which inherited Ace' will.
As for surpassing Yonko and Admirals, Luffy already beat the strongest out of those two groups, which is Kaido. He effectively surpassed them all. He won't fight Big Mom, he most likely won't fight Shanks. And I doubt he will fight all admirals. So he would at most fight Akainu in order to satisfy that statement of surpassing them all, at least according to your logic.
Can you answer a simple question? Whose underlings are stronger: Blackbeard's
Who by that logic should come later in the story?
Who in your headcanon will fight Akainu's underlings if Sabo fights Akainu? Sabo's underlings? Koala?
What underlings does Imu have? He only has Gorosei, who are old, incompetent farts and his strongest unit is CP0
The structure of the marines are different as compared to pirate crews. The 3 admirals and the fleet admiral are comparable in power. Akainu was marginally above Aokiji, Sengoku was at the very best on Garp's level, who was an unoffical admiral but stayed vice admiral in rank.
If Joyboy Luffy would have an all out fight with Akainu which goes into the extreme diff, then his underlings would not be able to beat the admirals, which happen to be near equal to Akainu. Who is going to take on the 3rd admiral? Jinbe or Yamato? So if Yamato or Jinbe beat an admiral, how is Akainu even remotely a match to Luffy, unless you believe the Akainu, who barely edged out his admiral friend, happens to be vastly above the current admirals, including Kizaru, who was part of the old team.
And as I said, the WG is already as highly alarmed as it gets, with Joyboy awakened, the order of the world crushed and the new generation being about to get the One Piece, with even Im himself being alarmed, as he holds Blackbeard's and Luffy's wanted posters even prior to Luffy awakening into Joyboy. And Akainu already said that he is going to participate.
So why exactly will the Marines and the WG in general wait for the winner of the PK throne to be decided, given it would put them into even much greater disadvantage than they are already in? They are already shitting their pants, as the world is leaving their hands.
The WG/Marines joining in will happen parallel to the next pirate moves.