Even though I believe that King is stronger than Katakuri now, remember that King and Katakuri have been pirates for decades. They both probably know each other and Katakuri most likely knows about King and his abilities.
Katakuri at the very least most likely knows how to fight King, we know Yonko crews have faced each other in the past like when Perospero and Compote recognized King or when Perospero told Marco that he always wanted to kill him.
So it is possible that they did clash in the past, also we have to remember that just because Zoro is having tough time against King it doesn't mean that the other YC1 would have the same trouble.
This is the first time Zoro is facing off against King, characters like Ben, Katakuri, and Marco have all most likely already faced off against King in the past.
The only major difference is that those were probably clashes and not an actual fight, like we are seeing here between Zoro and King.