First of all, let me state these points.

– Luffy and Zoro have always been close in term of Power Level, and they will still be when they reach their prime.

– Roger and Rayleigh were most likely the same as Luffy and Zoro.

– “One Piece: Vivre Card Databook” confirmed that Benn Beckman is almost as strong as Shanks! His card says that Benn is incredible powerful in terms of physical combat. The card even says that “Comparable to Red Hair’s, this man’s existence is feared by even the powerful warriors of the New World!!”

At the same time…

– Big Mom is clearly way more powerful than Katakuri

– Same as Kaido and King

– Same as Whitebeard and Marco

You get the point right? Luffy&Zoro / Roger&Rayleigh / Shanks&Benn, they’re more like DUO who grew stronger together. So it makes sense that they’re really close in power level.

On the other hand, Katakuri is Big Mom’s son / Marco is like Whitebeard’s adopted son / King and Kaido are likely in CLEAR HIERACHY like that. So, these First Yonko Commanders are way less powerful than their captains.

If you assume that each Yonko is close to each others in power level, then Ben Beckman would be clearly stronger than other First Yonko Commanders because he’s way closer to his captain. And this makes a lot of sense because of Yonko crew’s different structures. Big Mom/Whitebeard/Kaido’s crews are very large with infinite members, while Shanks’ crew is so much smaller (like Luffy’s and most likely Roger’s).

It was recently reveald that the Red Hair Pirates crew is the most well-balanced and impenetrable crew among the four Yonko crews and Shanks’ executives Beckman, Roo, and Yasopp have each won their own fame so it makes sense that Shanks’ First Mate is stronger than others’. A great showing of his strength is when he managed to take the arm clean off of the Worst Generation pirate Eustass Kid.