I think King and Queen are the closest to each other, and like you said much stronger than Jack.
That's not meant to downplay King, that's why Oda used Jack in their introduction as a point of reference to show that they are both absolute monsters, it's not that King is weak because Queen is close to him.
This is explainable by the meritocracy system Kaido has set up for his crew. Think about it, King and Queen are confirmed to have been a part of his crew since the moment he came to Wano. They are his main guys since his early days as a captain. Ever since then, for decades, they managed to keep those positions.
We see how the Beast Pirates challenge each other to take eachothers place and rank up, but no one was able to budge King and Queen from the very top since the very begining.
Once they go hybrid and they start showing off feats, these guys will be crazy