What Kid experienced in the New World, Luffy alteady experienced that in paradise
Luffy's journey has been far far harder than Kid.
Luffy fought 2 Warlords, 2 CP9 Agents, Megallan which took years off his lifespan, Admirals, lost his brother Ace( equivalent of killer dying) all before the timeskip.
What Luffy experienced pre timeskip is what Kid is experiencing in the New World.
This is why Kid pre timeskip said Luffy had a headstart compared to the rest of the supernova's.
Luffy has never experienced anything even remotely close to what Kidd has experienced in the new world. Maybe Ace’s death I guess lol.
Even Most of Luffy’s defeats turned into victories later on, with Luffy’s only real defeat in paradise being what Aokiji did to him, and what Aokiji did to him was pretty much nothing lol.
Kidd tried to fight big mom and got bodied by her children. Kidd tried to fight shanks and shanks’ subordinates chopped his arm off. Kidd tried to fight Kaido, and got thrown into a torturous prison for weeks after Kaido kept him as a trophy and force fed his right hand man a DF which turned him insane.
Luffy’s journey in paradise was a literal cake walk compared to that, and Oda needed to give Kidd an actual character arc to justify him being involved in this battle right now.
But no, we needed a poorly executed flashback about oden and the uninteresting samurai instead. I think I’m officially done pretending Wano is even a passable arc by general manga standards. Oda not giving Kidd a real reason for fighting is a fundamental failure that actually ruins anything Kidd is about to do in this final battle tbh.
Unless Oda later fixes Kidd’s arc and gives him some flashback reason for fighting, but by then it’ll be too little too late. For me, Wano is a walking corpse at this point.