This has yet to be disproven.
Yonko defeated characters stronger than YC1. Admirals never did. The closest thing they got to an actual victory was dabbing on injured King and Queen while subsequently getting wifi diffed by Shanks.
I am deliberately excluded Luffy here. Luffy is always a special case. He can lose to mid tiers and dominate top tiers depending on whether or not its his opponents time to go. Defeating Luffy is not a feat. Its a plot device to keep the opponent in the story. Once someone becomes on obstacle for Luffy the will get beated no matter who they are. Scaling by this is therefor irrational.
ZKK was a huge L because people went balls deep into it. A little reservation or humility would have gone a long way. Then again, I admired some guys determination about it. ZKK had valid reasoning behind it and all Sanji and Luffy fans were having sleepless nights over the possibility of it happening. I can not image the relief they must have felt when it did not happen.
I was also of the opinion that Zoro would play a huge role in bringing down Kaido. In a way he was, but not nearly as much as I thought he would be.
The one thing that irritates me the most about ZKK is the blue ball Oda gave Zoro fans with Hiryu Kaen.
It was the first and only move where top tiers started shitting bricks about and... it missed?!?!? Oda is a twisted old man.