It's there, so why do you inisist in disregarding it?
Just cause Kidd narrative has always revolved around the Emperors, you can't just exclude another plot when the hints are there.
Because it’s not pointing to Kid having any kind of grudge against the World Gov. It’s literally the only time he mentions them and it just shows a sardonic appreciation about how fucked up the state of the world is. There’s no sign he‘s enraged by this, no sign he wants to change anything, there’s nothing in his speech that hints to some sort of grudge with them, he just laughs about it.
And then every other scene with him has had him talk about the Yonko or Luffy.
We are discussing the most likely progression of the story, so what you care or don't care about in not an issue.
The progression of the story is that Kid has been left well and truly in the dirt by Luffy and Oda’s use of him in Wano doesn’t suggest he’s got much interest in delving deeply into him as a character.
Even if the case is of sharing the flashback with Shanks, what's the problem with it?
Doflamingo-Trafalgar shared flashback is an example of peak One Piece but seems like you're already labeling it as a trash secondary appearence on Kidd's part.
Secondary? No, Kid would be a... quinary? character in a Shanks flashback.
A Shanks flashback has to go through first of all, his childhood on Roger’s crew. Needs to establish his relationship with Roger, Ray and Buggy. Plus whatever happened in Shanks’ past before Roger that led to him being on the crew (is he Rocks son?)
Then we need to get his life as a captain of his own. That means setting up his fights with Mihawk and Blackbeard, and also how he met Beckman and set up his crew.
Then finally we need to get a bit of his perspective of meeting Luffy.
We also need setup for Shanks gaining the respect from the likes of Sengoku and the Gorosei.
All these relationships are more important than Shanks and Kid, which can honestly be dealt with as quickly as Kaido vs Moria was in Wano. Because really, the two are the same.
To Moria, Kaido was his great archnemesis who destroyed his crew
To Kid, Shanks is the Yonko who took his arm and he’s desperate to beat
To Kaido and Shanks, Moria and Kid are just some guys they fought with and wrecked in the past. They care more about the big boys like Oden, Blackbeard, Whitebeard, Roger.
It’s not like Doflamingo, where the relationship with Law was hugely important to both of them. Shanks has not once shown any interest in Kid. All he’s ever been shown caring about is Luffy and Blackbeard. I can guarantee you he wasn‘t going to the Gorosei to talk to them about Eustass Kid.