I see a lot of times people saying that people like Sanji and Zoro who don't get along are not rivals, but well this actually goes against one of the most famous stereotypes in Japan.
Japanese people always see people who don't get along as rivals, and this Is showed in numerous mangas, It has even become one of the classics of mangas having two guys who don't get along and who are considered rivals.
First example:
1. Near and Mello.
2. Beerus and Quitela.
3. Natsu and Gray
4. Yuno and Asta
5. Yami and Jack
6. Naruto and Sasuke
So let's check our information:
Mello said that he doesn't get along with Near because they've always been rivals.
So we know that rivals don't get along.
Second stuff we know Is that rivals can fight for everything.
People usually say that Zoro and Sanji are not rivals because they compete in stupid things so they're just gags, well that's not true.
In mangas rivals compete for everything, I mean even Naruto and Sasuke competed about who could eat faster, Beerus and Quitela did stuff like armwrestling and they share similar strength in combat, Yami and Jack from Black clover literally did not only armwrestling, but also a cooking challenge to see who was the best, and they also share similar strength.
Look this Is Yami and Jack from Black Clover challenging each other at doing stuff like cooking and at the end they want to beat each other:
An other video of them doing a stupid challenge but then having a serious fight:
If those characters share similar strength and have similar relationship that Sanji and Zoro have, why shouldn't our Sanji and Zoro be considered rivals?
If you ask, yes, japanese people see Sanji and Zoro as rivals, even in their pubblicitary spots they talk about them as rivals:
PS. Of course Zoro's a bit stronger than Sanji, we know that, but it's just like Mello (Sanji) and Near (Zoro).
Japanese people always see people who don't get along as rivals, and this Is showed in numerous mangas, It has even become one of the classics of mangas having two guys who don't get along and who are considered rivals.
First example:
1. Near and Mello.
2. Beerus and Quitela.
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3. Natsu and Gray
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4. Yuno and Asta
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5. Yami and Jack
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6. Naruto and Sasuke
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So let's check our information:
Mello said that he doesn't get along with Near because they've always been rivals.
So we know that rivals don't get along.
Second stuff we know Is that rivals can fight for everything.
People usually say that Zoro and Sanji are not rivals because they compete in stupid things so they're just gags, well that's not true.
In mangas rivals compete for everything, I mean even Naruto and Sasuke competed about who could eat faster, Beerus and Quitela did stuff like armwrestling and they share similar strength in combat, Yami and Jack from Black clover literally did not only armwrestling, but also a cooking challenge to see who was the best, and they also share similar strength.
Look this Is Yami and Jack from Black Clover challenging each other at doing stuff like cooking and at the end they want to beat each other:
If those characters share similar strength and have similar relationship that Sanji and Zoro have, why shouldn't our Sanji and Zoro be considered rivals?

If you ask, yes, japanese people see Sanji and Zoro as rivals, even in their pubblicitary spots they talk about them as rivals:
The Cup Noodle site updated with bios of the some characters from the commercial!
Zoro: A second-year high school that practices kendo. One year ago, At the National Kendo Tournament, he lost to his high school senior, Mihawk. Ever since then, he aimed to defeat Mihawk and become the world's best swordsman. Zoro constantly dozes off, and is late to school every day. He has a rivalry with Sanji and throws chalk at the teacher during class. Zoro never hits the teacher though, and gets hit with a ruler instead.
Zoro: A second-year high school that practices kendo. One year ago, At the National Kendo Tournament, he lost to his high school senior, Mihawk. Ever since then, he aimed to defeat Mihawk and become the world's best swordsman. Zoro constantly dozes off, and is late to school every day. He has a rivalry with Sanji and throws chalk at the teacher during class. Zoro never hits the teacher though, and gets hit with a ruler instead.