Zoro called toughest guy in crew. Toughest is a comparative.
Luffy never said "Sanji is the only one I can't become Pirate King without!"
or Robin saying "Sanji is the most important part; wings!"
And, again, Zoro has been called wings of Luffy by Oda. Similarly, Zoro has been called the one who acts as Luffy's Vice Captain by Oda.
Similarly, if Nami just said "Zoro is a really tough guy in crew" it wouldn't mean his endurance is better than others at all.
Luffy saying he can't become PK w/o Sanji means he can't become PK w/o Sanji, it has nothing to do with whether he can become a PK without other members or not. A similar situation just didn't arise with Zoro for Luffy to need to say that.
And it's subjective, words =/= portrayal. Zoro's actions are just as important as Sanji has ever done for Luffy, if not more-so. Think otherwise, give examples?
Again, you're, for some reason, making things said for Sanji more important than portrayal others got. Which is bullshit lol. Luffy doesn't need to say same shit to everyone.
Luffy literally, physically can NOT get to raftel or ANYWHERE related without Robin, yet he has never said that he can't become PK without Robin. So I guess Sanji is more important than Robin to his dream? Even though Robin is literally a necessity that can not be copied or replaced by any means?
Please, characters just get their spotlights in unique way. Luffy's statement in WCI and Robin's comment was Sanji's way, and it is irrelevant to spotlights other characters got.