My perspective on Oda's mistakes regarding Luffy vs Kaidou, and few suggestions (wishful thinking and wank) to make the storytelling and powerscaling better and earned. Here we go:
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1. Recklessness from the start
- Luffy acting impulsive in Udon, at the first meeting with Kaidou.
The solution: Saving FS, facing a Yonkou, Luffy should've instead realized that every possibilities of the Future if he try to fight Kaidou, is death. Not just his death, but the massacre for his comrades first (imagine seeing Zoro, Sanji, Nami, Robin, Law die in front of him, their bodies exploded into meat juice as Kaidou deathblitz them all, with just a single move, his speed to kill them less than a hundreth of a second.) and he saw his own death the last. This emphasizes both Luffy's FS and also Kaidou being WSC. The win-win solution for hyping their future battle.
That way, Luffy will wreck his own brain lightning-fast to bring his friends to some hideout in Wano first (before Kaidou closing in on them) instead of even encountering, much less confronting, the WSC directly. His friends will be confused as Luffy seem to know which way to go to and which direction to avoid in order to finally escape something that they havent even sense yet, which Kaidou's presence and attention.
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2. Lack of individual preparation and self build-up
- Luffy is facing the literal Strongest Living Being. He cant just go wherever he want and fighting fodders and Ulti and Page 1 and Yamato and Queen etc, he is the last stand against Kaidou for Tonjit's sake. He shouldve preserved his strength, move as efficiently as possible in this arc. Only fight himself if its absolutely necessary. Which, with Zoro-Law-Kidd-Yamato backing him up, they wont let anyone near him. If King-Queen-Jack can be fought against 1v1, well Luffy shouldnt even participate in fighting them, and save his strength only for Kaidou since the start.
- Luffy is facing the literal Strongest Living Being. It is foolish to train in prison, after defeat. The wise action is for Luffy to train individually since the start of post-timeskip, in order to defeat Kaidou. Bring us a flashback of Luffy being oddly silent and locking himself in the Thousand Sunny's Captain Room, hours and even days after each arc battle. Against Hody, Doflamingo, Cracker, Katakuri. During which, he evaluate each of his strength and weaknesses, and constantly went under image training against the enemy he just beat, finding the best possible scenario to beat them efficiently to correct his mistakes...and more importantly, to do the third keypoint from me, that Luffy severely lacked, even when he should've made himself the best in the One Piece World regarding this:
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3. Too much Messiah and Destiny - Lack of Creative Process - Luffy's Power Invention.
If there is something really impressive about Luffy, it's his creativity to invent his own powers using whatever assets he possesses, into something really fresh, fun, and at the same time limit-breakingly powerful. Imagine using one of the most boring and weakest Devil Fruit, Rubber Fruit, and instead formulate Gear 2nd. Imagine seeing it at the first time. Even without proper process and hints, its application in battle was nothing short of incredible. Now Luffy should've trained his creativity and Oda should've (to some extent) depicted him as a boy that is hinted to be mentally exhausted, some time before each important battle. During his movement to reach Kaidou, while he shouldnt even participate in other battles...in contrast, his mind shouldve reeled constantly. Since he must push himself to formulate the strongest power possible, he cant relax since it's the WSC he will fight against. He shouldve told himself, its to protect everything. He can rest once its over. Its to protect everything. He can rest once its over.
During Luffy vs Kaidou, Nami or Zoro or someone shouldve told other alliance members like Scabbards, or having an internal monologue, that Luffy was exhausted before this battle against Kaidou even begin: since Luffy seemed to constantly invent and do experiment of his own fruit-haki-body-energy-mind etc to escalate his own powerlevel, and also constantly re-evaluating his own ideas on that, in order to surpass his enemies with his original ways.
This way, Luffy didnt need to emphasize the fated Voice of All Things as something to help him in dire needs, such as when Kaidou threw him down from Onigashima. Luffy shouldve faced Kaidou with his own original powers, maybe he managed to invented Internal Destruction as the result of his power invention? Instead of Hyogoro teaching him? That way it felt earned. Yes i'm looking for that feeling of Luffy earning something instead of taking that CoC specialization notion for granted.
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4. Too much intervention for hyping up others
Luffy vs WSC Kaidou, is the battle for PK. Just like Zoro vs Mihawk is a battle for WSS. Oda shouldve make it clear to everyone that Luffy vs Kaidou is not a battle they can interfere without their own death as the only result. Make Kaidou oneshot Zunisha as revenge for Zunisha oneshotting Jack, so everyone recognize that Kaidou is an existence with an impossible powerlevel beyond their imaginations. Make Kaidou state "This is first warning, and also the last." or something signifying that he, Kaidou, holds the life and death of the whole alliance, at his mercy.
This will be a solid pay-off to Kaidou's WSC introduction build-up. If Kaidou oneshot a living island then what can they even do lol? Oda should pay his respect to Kaidou this way, not making Kaidou relying on hostage since Oden must be wanked as well lol. Pick your priorities clearly please, Kaidou is a strength-epitome arc boss who btw also decides he wanna be PK. Its an exclusive battle for Luffy. Make it so. As for the others, they can fight BM. Oda can make Orochi as an extremely proficient swordsman who is also a menacing hydra etc, for Zoro to fight against for example. If Zoro absolutely must fulfill dragon-slaying legend as his role, then make Orochi have Seiryu Devil Fruit instead. While Kaidou can be designed to create his own powers with mystic sacrifices or absorbing a hyper mythical artifact or something and assimilated its powers with his own, Original Titan powers or something, something worthy of WSC. Whatever, doesnt even have to be a Devil Fruit in order for Kaidou to achieve his WSC status, Oda can always find another way actually.
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5. Earned powers, Earned Loss
Then after this much preparation and build-up, Luffy can earn his powers, he can battle to his heart's content, THEN he can lose. I agree that Luffy shouldve be beaten in Onigashima battle against Kaidou. But only with point 1-4 fulfilled. Not without. So Luffy' Onigashima defeat shouldve been his first and last, against Kaidou. No fake tension moments, no empty hypes, but an actual WSC and earned powerup, also Luffy becoming the one we actually root for to win an impossible fight, and he lost after all. A whole-hearted defeat that happen even after Luffy prepare himself to the utmost. In exchange, Oda shouldve replaced Kaidou oneshotting Luffy (Udon), with Luffy making strategic retreat instead (see point 1).
6. Finding Out Ways to Heal and Formulate the Final PU
Luffy can heal himself with meat. Gag moments right? Not for me. Oda shouldve gone all the way and make that stuff a doorway into Luffy figuring out that he can make his rubber body metabolize nutrients extremely fast, converting all of it into protein regeneration and strength-muscle-building or whatever. During that process, Luffy also formulate his last powerup. It can be achieved from figuring out that Ragnarok had CoC infusion. But Luffy doesnt stop there, he acknowledge that just copying his enemy's CoC Coating techniques will not grant him victory since his enemy can also do the same. So Luffy takes a step further, and make something never seen before in this world. It can be Internal Destruction CoC, like Rupture2 powers made entirely from CoC infusion, or it can be compression-based kinetic energy manipulation, whatever, something only someone as creative as Luffy is capable of. So once again, that Luffy' victory feels earned.
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Sorry, cant resist.