Oda strongly hinted that Zoro and Sanji are close to each other in Strength!

1) The beginning of the rivalry : Little Garden : Dorry and Broggy

In the Little Garden arc, Zoro and Sanji’s rivalry begins when they bicker about who is better at dinosaur hunting. They hold a contest to see who can hunt the bigger dinosaur. Pretty fun stuff.

But what do you know? We later come to know that 2 giants named Dorry and Broggy have been fighting on this island for 100 years, with neither of them being able to kill the other and have had equal number of wins.

It is initially said that they forgor the reason for why they were fighting in the first place, but it is later revealed that…

This whole fight was over who hunted the bigger fish. This is clearly a parallel.

In the same arc that 2 warriors have equal, endless fights over a hunting contest, 2 people start a rivalry… over a hunting contest.

So it is clear to me that Oda is setting a parallel between Dorry/Broggy and Zoro/Sanji and is trying to convey to us, that if Zoro and Sanji were to fight it will be like Dorry and Broggy.

2) Oda refuses to answer

A fan asked a question in an SBS. And Oda not only avoided the question, he have a classic Oda answer.

D: If Zoro and Sanji had a serious fight, who would win? Zoro beat Mr. 1**, so… he’s stronger, right…?**

O: Whoa! That was surprising… I thought you said “If Zoro and Sanji had a dick fight”…You have to be careful what you say. Someone might hear something totally wrong… Okay, see you next time!!

Huh? Why would Oda avoid something so straightforward ? Unless… he doesn’t want to be straightforward. He straight up avoided answering a Zoro vs Sanji question… make your own conclusions.

3. Doriki

I know Doriki is not exactly a reliable method of powerscaling. But let’s step away from in-universe explanations, take a step back and jump into Oda’s mind.

Why would the Doriki’s of Zoro and Sanji’s opponents be so close to each other? Oda could have easily made Kaku’s be 2500, and Jabra’s be 1900. You know, create a good gap between those two, while also maintaining a big gap between the rest of CP9. But no. He almost made them dead equal.

Why? Make your own conclusions.

To me, this is how Oda sees Zoro and Sanji. Zoro being stronger, but ever so slightly. Just like the Dorikis of Kaku and Jabra. And just like the bounties of…

4. King and Queen

Yep. Here we are. Just like with the Doriki system, Oda could have made King’s and Queen’s bounties be super different. But he chose to make them super close to each other. King’s bounty is 1.39 Billion while Queen’s is 1.32 Billion. A measly 70 Million Berry Bounty difference.

Now, I know bounties are not accurate powerscaling tools, but I speak solely about portrayal at this time. Zoro and Sanji beat 2 people who have a very low difference in bounty, just like Zoro and Sanji beat someone with a very low difference in doriki.

5) The height differences of rivals

So Oda does thing this where rivals have very low difference in heights, of just 1 cm.

This provides further credence to my points.

Other points which I think is worth being talked about, but these are in no way strong points, so take them with a bigger pinch of salt :

Zoro and Sanji taking out a Pacifista together while Luffy got one on his own.
Wings of the Pirate King.

Both of them being the ones to make Oars fall in Thriller Bark by making him lose his footing.
Fighting opponents who bicker (DazBones/Bon Chan, Kaku/Jabra, King/Queen).
Constantly portrayed as a duo.