Oda goes as far as to account for the rivalry between these two even when designing their characters
Making them both the same age.
Making their pre time skip character design so that Zoro is a single cm taller.
Making their post time skip character design so that both have the exact same growth spur and Zoro remains a single cm taller. That's to say "Look idiots, i'm viewing their dynamic the same way as i did before".
Anyone claiming that Oda does not think about Zoro and Sanji's character with their rivalry in mind, is absolutely clueless.
The very first interaction Oda writes for Zoro post time skip is with Sanji
With Zoro turning even the order of their arrival into something that he'd brag about to compete with Sanji and claim superiority.
Of course there are many gag moments involving them, but that does not mean that them being competitive with each other is not a legitimate part of the story, and their rivalry is not a real thing.
Oda went as far as to draw direct paralels with a century old rivalry between giants, and maded it so that the competition between Zoro and Sanji in the same field yielded the same results.
They get competitive towards each other when it comes to their
Bounty
They get competitive towards each other when it comes to their
Strength
Fresh "out of the oven" examples focusing on defining elements for their status as Pirates and Fighters.
It's mind blowing to see people attempt to draw paralels with the type of interaction Shanks has with Buggy to discard Zoro and Sanji's rivalry being in any way relevant for how the two compare strength wise.
In the case of Zoro and Sanji, the stronger of the two, also get's competitive about all of these things. Zoro feels strongly about proving to be more powerful. Zoro feels strongly about having a higher bounty. That's why he gives self praise when someone else talks about Sanji's strength. That's why he lashes out when Sanji talks about him having a higher bounty.
Adult Shanks absolutely does not consider Buggy a rival in that same way. The fact that there are people disingenous enough to go ahead and argue the opposite, shows how they lack credibility when it comes to talking about how Zoro and Sanji compare and interact with each other on any level.