"This is shonen and 1 vs 1 is next after 2 vs 1" is not an argument though. Nothing good awaits Law and Kidd, especially since no time has passed since the 2 vs 1 for them to progress at all.
How is that not an argument? One Piece is following basic Shounen rules, it initiated them pretty much. Like Luffy beat up Katakuri and went for Kaido in about... how much days? The same happens here with Kid and Law. It always happens in shounen. Doffy - Katakuri - Kaido... heck we can pull up every fight of luffy or any other person in the crew (beside timeskip) and always have just a few days inbetween.
So, how is that not argument?
Luffy also said he wants to beat Big Mom and nothing came of it technically. One is Kidd's perspective, and the other is narrative reasoning, which in this case is the poneglyphs.
The narrative reasoning about Shanks getting poneglyphs and going for the PK title doesnt exist. NOBODY has claimed it in 25 years, before shanks suddenly says it x chapters ago (dont want to count, but its not even 15 chapters ago). There is no narrative in which this has to take place, it doesnt even makes sense from beginn with. Remember the confusion when the chapter dropped? Nobody expects it and narrative wise, it still makes no sense. Or where was the narrative >15 chapters ago?
Scenario: Kidd beats Shanks, what is the result of this? Kidd gains nothing but more fame I guess, Shanks gains nothing. Then they would have met for no reason, that's not possible.
Kidd gets his major power up, CoC mastery.
Kidd gets Yonko title.
Kidd gets presented as strong warrior on elbaf, additionally for him getting the aknowledgement for taking Big Mum down, so he gets territory and allies ("Grand Fleet).
He most likely would get the full fetched Yonko title.
Shanks would be put in the perfect position for Blackbeard coming for his head, like BB did with Whitebeard.
Shanks would get his confidence in the new generation, like Whitebeard got with Ace/Luffy.
Shanks would get his place as mentor for the new generation, not only for Luffy.
....
Alot of reason for both of them here.