Zoro has nothing to do with Luffy, who is the whole focus of this story; don't even compare those two, all this manga is built around Luffy. Sanji doesn't need to pretend to be a conqueror, he still gets everything Zoro lacks and actually takes time and effort, starting by interest from the author to work with his character.
If you think Zoro having conqueror's haki shows more interest from Oda than everything he has done with Sanji since Zou (don't even need to count before that) then you're deluding yourself. Zoro isn't irrelevant, he for sure is an important piece of this story, but the treatment he has been given by Oda is ridiculous in comparison.
We entered Wano with huge potential for Zoro; ended up wasted.