Well its just clear Zoro = Rayleigh 2.0. He is like Danzo or adult Sasuke in Naruto/Boruto, a Shadow Hokage. So in some stats he is above Luffy, in others below.
I've lost count of the amount of characters whether they be spectators, rivals, allies or villains that have remarked upon Zoros strength and abilities. There is consensus that a man of that calibre doesn't follow anybody else, he already has the ability to be a Shichibukai or (further on) Yonko by himself. And that speaks volumes of his captain, to have a guy like that as his no 2/partner.