Omen Sommers easily blocked Dragon Damnation. That is a feat that neither King or Lucci can replicate.
He is clearly the strongest of the three, so the answer is infront of you. Current Zoro treats Lucci and King like fodder.
As a matter of fact, we already knew King was fodder to Zoro since he unlocked King of Hell. The second Zoro figured out King's gimmick and unlocked CoC, he easily dealt with him.
I never thought Lucci was truly ever close to Zoro in strength to begin with and King was defeated by the very move that Sommers easily blocked.
They dont need to replicate it to be stronger than Sommers - this is what you arent getting.
Current Zoro is the same Zoro that faced King.
Zoro was lucky that King went into flameless mode, aCoC merely allowed him to negate King's physical superiority, to prevent him from slapping Zoro around with his powerful moves.
Zoro didnt need to overpower Gram to treat Sommers like trash by stabbing his heart effortlessly. He aint that easily doing that to King and Lucci. Just because Gram can overpower powerful moves, it doesnt make the wielder powerful. There is far more to combat than just that. As you should have noticed, Gram didnt save Sommers last chapter.
King would trash Sommers easily, even Lucci would.