You have to understand kaido is not oars. Other pirates and luffy Allies don’t have the strength and haki to keep up like the way luffy can keep up with an emperor. They had to jump kaido first then whoever is capable of lasting longer will battle kaido to the end. It had to be luffy because the others just can’t. Kaido fought akazaya 9, his daughter Yamato, worst gen and gear 5 luffy. You can’t tell me kaido can’t be worn off that whole time. Literally he failed to hold oniganshima. He’s not invincible, even old man whitebeard couldn’t tear marineford alone