Oden: They are the ones who can strike down kaido!!
White beard: You think you can vanquish the man... that kouzuki Oden could not?!! don't be conceited ace!!!
Kaidou openly made a statement about all people that would include who would be the person who could take him down in the future, and his final conclusion was that Joyboy would be the man, without Prime WB, without Shanks, without Roger, without Navy or government.
Kaidou stated that no one in the world was capable of defeating him, this includes all of the higher ranks today, and he wasn't wrong because NIKA/JOYBOY didn't exist until Kaidou killed Luffy.
Kaidou is so strong that even KING doubts that JOYBOY he's been familiar with from the stories since he was a child will be able to defeat Kaidou.
Something that King has consistently said:
The embodiment of strength in the last 10 years after the GOD VALLEY incident.
Admiral Aramaki: "If kaidou were here, I wouldn't even have come, he's the one who kept the enemies away from Wano country."
Orochi: I din't ask you if it was possible or not. celestial dragons ? Navy? You must know...
that the country of wano does not fear these things.
I have kaido backing me up!!!
Blackbeard: Meanwhile, events are taking place in wano, where the
dreaded monster Kaido lives!!
Government: With the slightest chance of Kaidou falling, the government wanted to conquer Wano, but they didn't even dare enter the country while Kaidou was still in charge of Wano.
Government: I can't see Kaidou defeated.
Government, but precisely the 5 elders: So we've lost an elite agent...and made kaido angry,what was the point ?
Government: you want me to inferfere with kaido's battle ?!
that's impossible!! they know full well it's impossible.Trying to stop Kaidou's confrontation with the government is seen as impossible for obvious reasons, they don't want to provoke Kaidou's fury.
Sengoku and Marine: He earned the respect of ferocious pirates through his individual stength alone...