In fact, Luffy's current strength was already very close to the level he had reached when fighting Kaido two years later in the original story. It could even be said that he was somewhat stronger.
He had developed the Three Colors of Haki, Conqueror's Haki Infusion, and Future Sight through Observation Haki. He had also mastered Gear Fourth Rubber Man.
Even in terms of physical strength alone, Luffy, who had received better training since childhood, was slightly stronger than his original counterpart.
Together with the rest of the Straw Hat Crew, their lineup was already very close to that of a Four Emperors crew.
The arrival of such a powerful force, one that was nearly at the level of the Four Emperors, dealt Kaido—who had previously held a slight advantage—another vicious beating.
But soon afterward, perhaps due to the will of the world or something of the sort, Golden Lion joined the melee as well and formed an alliance with Kaido.
Their reason was to obtain the Poneglyphs collected by the Dragon Hunting Pirates.
This protracted war lasted for over a year. During that time, the Red Hair Pirates and the Spade Pirates intervened, deliberately or otherwise, preventing Luffy, Yamato, and the others from being crushed by the two Four Emperors crews right from the start.
In truth, the other members of the Dragon Hunting Pirates had been keeping a close eye on the war all along. Yet Luffy and Yamato, who had initially been at a disadvantage, grew at an incredible pace amid the fighting.
Luffy in particular. During one crisis, Golden Lion used the Float-Float Fruit to carry the entire Straw Hat Crew into the sky, then joined Kaido in besieging them. Pushed into a desperate corner, Luffy awakened his Nika Fruit. He fought one against two for