What Zoro did regarding Usopp post-EL was important lesson for leadership and no other crewmate has confronted Luffy in that manner.
Constantly keeping Luffy in-check, reminding him what's important (Right after Usopp fight, EL, PH, etc) is something only Zoro does.
Oda deliberately chose to make Zoro take all of Sanji's pain in TB rather than have Sanji and Zoro share it.
Oda deliberately chose to make Zoro constantly support Luffy on the roof-top while leaving Sanji out of it.
There are many more examples. Sanji got those statements, meanwhile Zoro has many actions related to looking after Luffy and keeping him on track which others simply don't have.
I'm not saying one portrayal is better than other, but you stupidly claiming Sanji is more important to Luffy's dream because he's called wings? Or because Luffy said he can't become PK without him? You think Luffy wouldn't say the same to, say, Nami or something? C'mon. Of course he hasn't said that to Zoro, either... why in the world would he? Zoro has been unwavering and on his side since day 1; Luffy doesn't have to say that to Zoro.
On another note, Oda himself called Zoro one of Luffy's wings, as well, in SBS. So there's that?
Luffy said he can't become Pirate King without Sanji. Luffy also said he can't do everything and would not make it without his Nakama in general many times before.
Idk the fuck you're trying to compare at, man. Sanji gets shine and portrayal of his importance to Luffy in his own special way. So does Zoro, so does Nami.
They're not supposed to be portrayed in an identical manner in identical statements and light because they're different, yet just as important to Luffy. So why are you asking me "well, they said this thing about Sanji but not for Zoro! So Sanji more important?!"
Learn to read the story, dude. Quit trying to shoehorn other characters into a narrative made for a separate character.
All Nakama are important for Luffy's dreams and in this or WCI scene Sanji is absolutely not given importance over other crewmmates in that regards. He's given importance. Not comparative importance.