Man it's crazy that King has got the acknowledged of many other YC level pirates like the BM pirates and Marco as well as Queen as formidable. Even motherfucking Big Mom did too. All he needs now is for Kaidou to acknowledge him (on screen)
A good scenario is for King and Zoro to COC clash which causes a shockwave like Luffy an Katakuri did (and maybe split the sky) and then Kaidou is like "that's my right hand man"
To be fair, when Kaido announced that the Flying 6 could challenge the Calamities, he turned to King and jack who were at the scene, with a grin smile that could indicate a LOT of confidence on them to keep their status.
Kaido values strenght. He builds his entire crew around this stat. King and Queen were with Kaido even by the time he reached Wano.
I think words are unnecessary. Kaido holds his Calamity on high regard.
If he was excited to show Linlin how "strong" the Flying6 were, but still thinks his Calamities can easily keep their status, you can already assume how much Kaido values their strenght.