I'm not a Sanji fan, in case you thought so.
What proves that Zoro is stronger than Sanji is that he gets a stronger enemy to fight (call it Bonez, Jabra, King or whatever), that he's Luffy's right wing, that he's usually second in bounty and so on; THAT'S what proves his superiority.
This scene is so obviously written in order to stress Sanji's suffering with the situation, to the point of asking freaking Zoro to kill him in case he goes evil, that your philistine lecture hurts; the point of this situation lies on the kind of, yes, BROTHERHOOD that rarely happens but Oda consistently uses to emphasize the importance of a moment. They are frenemies, they love each other just like any other Straw Hat, and they share powerful trust deep inside (Enies Lobby, Punk Hazard, Zou, even in Wano we had Zoro trusting him enough to sleep while defenseless). So, when you have Sanji asking him to kill him if things get ugly, you are expected to APPRECIATE the moment and the dynamics between them, period.
You guys are so fucking poluted by your delusions that can't even appreciate an honest moment of friendship. YOU are the fucking clowns, laughable dumbasses who believe Oda wouldn't absolutely despise the way you read his work, as if you are so non-functional that can't read a piece of literature without turning it into a RPG.
Fucking useless people, for God sake. Hope you are as irrelevant in your real life as you are in your virtual one so decent people won't have to suffer your braindead approach at being human.