i agree with the first part, kid and law didn't take a lot of damage and didn't go all out as opposed to luffy and zoro.
as for marco, he suffered a devastating defeat by teach in the payback war made him retire from the pirate life for good, so no, he's nowhere close to be a yonko, a YC1 at best.
kaido is known worldwide , katakuri only known among his family and crew.
yamato never doubt kaido, she just placed her faith in luffy, it doesn't go against kaido's invincibility in 1v1 battles, and she already stated her concerns to that matter previously.
also to go with the 1v1 thing getting debunked in the future by luffy; isn't kaido being unkillable an established fact and serious claim that needs to be challenged, and we know that luffy doesn't kill his opponents, so someone else has to break that belief, zoro is the prime candidate, especially with all the build up around him being the second coming of ryuma, the legendary samurai that slayed a dragon.