What nonsense are you saying? Kaido stating that Luffy could go 1v1 against him doesn't change the fact that Kaido received damage and expended stamina against other people earlier, man.
Luffy was in a worse condition solely because of facing Kaido, and it was Kaido who left Luffy in that state. Kaido was in worse condition not only because he faced Luffy but also a series of adversaries.
Kaido faced Yamato = expended stamina during the fight against Yamato.
Kaido took attacks from Ashura Zoro = had part of his stamina drained.
Kaido received another series of attacks that had some impact in the end, besides, of course, expending energy against the Scabbards.
You just need a bit of rationality. LOL
Unless, of course, you believe that Kaido's fights against the Scabbards, Yamato, and the SNS on the rooftop didn't affect his stamina at all, and he remained unchanged, and it was Luffy who did everything by himself. LOL
Also, Luffy and Kaido being in the same condition doesn't mean anything because their exhaustion was reached differently and not through a 1v1 from the beginning for both of them. Luffy exhausted himself solely by fighting Kaido numerous times, whereas Kaido exhausted himself not only by fighting Luffy.
Kaido begins the arc by fighting against 9 people who aren't Luffy = This costs him some of his stamina.
Kaido then fights against 5 people, 4 of whom are not Luffy = This takes a toll on Kaido, and Luffy contributes to draining Kaido's stamina here, but he's not the only one.
Kaido then has a 1v1 against Luffy and wins = It costs Kaido some of his stamina.
Kaido fights against Yamato = This depletes Kaido's stamina.
Kaido defeating Kinemon again = It costs him something.
Kaido finally engages in another 1v1 against Luffy = It takes a toll on his stamina.
Kaido descends from the rooftop and starts attacking the alliance = This depletes his stamina.
Kaido finally returns and fights against G5 Luffy = He loses.
Kaido was drained differently compared to Luffy, who only reached his limit by repeatedly attempting to defeat Kaido.
To make this a fair 1v1 in my eyes, we would need to remove all the other people who aren't Luffy and who had their contribution in draining Kaido. The Onigashima arc would have started with Kaido vs. Luffy, and every time Luffy was defeated, Kaido would have remained still and rested instead of constantly running around and fighting opponents who weren't Luffy. This is without considering whether the island was draining Kaido's stamina or not.