Think of it like this.
Imagine a bird with 2 wings and one wing isn't equal as the other. Bird loses balance, can't fly as good, it steers off.
Both wings need to be equal in order for the bird to fly properly
That's not the analogy. You're taking something symbolic and turning it into what's written literally.
Birds have dominant wings, too, just like people have dominant hands. When you're doing something with both hands- such as lifting or this or that, then both hands clearly exert equal pressure and one doesn't matter over the other, same as birds flying. But point remains that, narratively in a story, a right hand will ALWAYS be more significant than left hand. Not to say left isn't incredibly important, either.
And it is shown throughout the series. I'm not even going to bring up combat-based stuff because that's irrelevant to the narrative I'm speaking off:
- Zoro is the one who takes Luffy's pain. Sanji aims for it alongside Zoro- as Luffy's another arm/wing, but ultimately it's the right hand that takes it. They were not written to share it equally like every other shonen or story would do to show narrative equality. They're both shown as the final two pillars, yet Zoro is the one that stands at the end.
- Zoro is made part of Worst Generation; the group portrayed as spearheads and leaders of the new era for hundreds of chapters now. Sanji wasn't included.
- Roger has Gold, Silver and Copper to represent M3 parallels, as well. A silver will always be > copper.
- Most parallels of significant enemy/deuteragonist groups include Luffy/Zoro as parallels. Be it Smoker/Tashigi, Crocodile/Mr-1, Coby/Helmeppo, Garp/Bogard, Kidd/Killer etc, etc.
- Zoro being the ONLY one referred to as right hand of Luffy over and over by different characters, etc. Canonical materials such as VC put even more emphasis on it.
- Zoro getting CoC, being a Conqueror. He had fuck-ton of foreshadowing regarding it, as well.
And many more, honestly.
That does not mean parallels between Zoro and Sanji don't exist.
They do- as they are Luffy's main two pillars of support, so of course they'll have multiple parallels of such. But Zoro has his own exclusive narrative significance and importance that puts him a step above Sanji in terms of both crew and specially story-wise.
Again, this is not me shitting on Sanji. Sanji is definitely part of Monster Trio. Sanji is definitely very strong, and Sanji is definitely very important to Luffy, and the crew as a whole ahead of everyone that's not the Captain or Zoro.
But ultimately, he is the left hand of Luffy and among his two biggest pillars of support alongside Zoro.
And Zoro will always be the right hand of Luffy, and the last standing pillar, as evident in TB. And story-wise, narratively, Zoro has significantly more going for him with CoC and WG, too.
And some "wings" comment that also existed in SBS years ago wouldn't change that lol. Wings is symbolic to represent Zoro/Sanji as two main men for Luffy. No need to take something symbolic LITERALLY (bird can't fly w/ heavier wing wat) all while ignoring the narrative that has been built up again, and again, and again for years now.