You said it yourself, it's after the time skip, i.e. at the time skip Oda thought of a way to contrast the two further with Zoro's eye. It's an aesthetic contrast not a functional one.
I don't know about other people but I didn't say they were polar opposites just that they contrast each other a lot like 2 sides of the same coin, plus as Corazon said if he remembered correctly Oda refers Zoro/Sanji to Luffy's "wings" so it's like two halves make a whole, add Zoro and Sanji the way they are represented now and you get two visible eyes and someone who uses legs and arms, if it helps you you can think of them as a Ying Yang and the eye is the dot. Even though they have contrasting characteristics they're complementary.
"Zoro's scar being some kind of a pair with Sanji's flowing hair is a joke."
This line here makes me think you didn't get the jist of it.
The scar and the hair have nothing to do with my point, my point is sort of like you said Zoro and Sanji are very similar yet they have these core contrasts between the two of them, I think Oda decided to have Zoro's eye be closed in the story to draw a parallel between him and Sanji who are both essentially Luffy's left and right hand(when it comes to fighting)
Getting the gist of it? The gist is Zoro has his left eye closed and Sanji has the tendency to every few years or so sweep his hair to the other side of his face making his eye difficult to see, which happens to be his right side now. And you see in that some kind of an almost certain fact that Oda intentionally did that to symbolize the 'contrasting' relationship between the two. What is there difficult to understand about it? And then I refer completely back to my first post on how that is a joke and that it's just you that wants to see it that way, but that in reality there is barely anything that backs it up as the reasoning you used can be used to say the same thing about a lot of other characters as it's an extremely shallow and subjective interpretation.
Fujitora has lost both eyes and he is a swordsman, this MUST be a symbolic visual statement of the relationship between Fujitora and Zoro, that Fujitora is his father or something. When the timeskip just happened, people were also going on about how Zoro's scar matched that of Rayleigh's, which they said was supposed to symbolize the relationship between Luffy and Zoro as how Rayleigh was to Roger. And you can go on and on about this.
As a visual contrast this is indeed a joke. Now if it happens so that Sanji would have a scar over his right eye, now then try again. But saying that Zoro has one closed eye and Sanji having his hair covering the opposite one as an intentional visual representation of a non-existing contrasting relationship, yes I find that a joke when you then at the same time are going to act that Zoro becoming potentially stronger if he would open that eye is too far-fetched, while that what you say does not have much more or even less going for it, but act like it's clear as day.
Zoro and Sanji don't have a particular contrasting relationship, if anything they seem to butt heads with the parts of their personalities that are similar, and there is no reason whatsoever to symbolize on their faces this supposed contrast and even less with such a bad one. Contrast and opposite are pretty much the same thing here as you can't have a contrast if two things aren't very different. If you are going to see a difference there, you pretty much admitted that you only see what you want to see as all the Strawhats would be contrasting with one another following your own logic, but you only decide to look at Zoro and Sanji. Same thing with your comment about the scar. Saying that, you reduced this all to that Zoro has one eye closed, Sanji has something covering his other eye and that is then Oda intentionally trying to visually represent their relationship. Seriously the more you read all of this, the more obvious it becomes how feeble this entire reasoning is.
The comments of those wings and coins are also very misplaced and don't make much sense as again you can interpret them in so many ways, it's useless to mention it. For instance I can interpret that as that Zoro and Sanji are supposed to be nearly completely identical, have to flawlessly work together and that one can not exist without the other. But in the series they continuously argue with each other. That you are going on about how one is using his hands and the other his legs, is almost childish. Zoro uses swords, which are most easiest used with your hands. He however also uses one with his mouth. I'll eagerly anticipate the day I see Sanji choking a man to death with his ass. Not to mention Sanji has used a bladed weapon before, he simply does not use his arms directly as he needs them to cook. He however uses them passively in some moves, just like how zoro needs his legs to move his body. Even among martial arts that solely focus on using your arms, the movement of your legs is crucial and vice versa. Not to mention are Zoro and Sanji the only characters who use their arms and legs to fight?
You see what you want to see. Again if I follow your logic and reasoning I can do this: Zoro and Luffy both have a scar on the left side of their faces and a scar on their chests. This clearly shows that Zoro is Luffy's closed companion, that Zoro is higher than Sanji on all aspects. I just ended, using your logic, all the debates about Sanji vs Zoro. Zoro is simply the strongest, the vice-captain, the Nr 2 of the Strawhats. He is higher than Sanji. It's clearly visually represented by Oda on their bodies. Case closed. Now if you don't agree with this, you can't agree with your own reasoning as this is what you did.
