Kaido is just too strong to be defeated alone. Big Mom it's not the main villain so she's not as important. Besides, Big Mom has kind of turned into a joke character. Look how many times the straw hats have embarrassed her.
Ok so Didn't Kid and Law fight Kaido as well. I know luffy did much damage to Kaido than them but It would be really sick if luffy wins after getting knocked out more than 5 times and even when Kaido isn't at 100% and didn't even rest for a minute. He has been fighting continuously for chapters.
Nah unfortunately not.. Hardening on body should be harder than invisible hardening yup? CRACKER used it with his shield so thats different even doffy couldn't harden the entirety of his cloak into black.
Because they know Zoro and Sanji are Luffy's top fighters and they won't want one of them to recover since he's already down. It's about using their brains, not praising him as someone capable of installing fear into their hearts.
Marco gives up when in front of King and Queen at the same time and he's already exhausted enough for Perospero to notice it from the distance while still having a 2 versus 1. If anything, the only valid conclusion you can extract from this is that King had it easy and still wasn't capable of winning by himself.
It's not like this matters, anyways. The clear message is that Marco exhausted his abilities and had trouble to keep fighting because, as he commented, it's hard to face two billion combatants at the same time.