Lol at same things would have happened if they switched opponents because i said so. Sanji clashes with Doflamingo, uses his high end attacks, unable to push him an inch back. Zoro uses a one handed slash on a stronger opponent, pushes him several meters back. He'd have overpowered Vergo. He may have lost to Doflamingo though, but he'd have put up a better fight, i guarantee it. Concurrently concerning Zoro's opponents, while it's true he'd have defeated Monet without much trouble, portrayal counts here. Tashigi saw Sanji fight Vergo, but the one who astonished her by his strength was Zoro.
Furthermore, Zoro may have defeated Pica without much troubles, but Zoro isn't Sanji. It's like saying Vergo is weak because Law cut him in half the moment he got his heart back. Someone who is weak comparatively to Zoro doesn't make him weak comparatively to Sanji. He looked weak because Zoro was that strong. Pica specifically was hyped as the strongest top executive on dressrosa with Viola saying he is the most dangerous one, with Fujitora calling him "dangerous", with him being portrayed as a threat to the entire coloseum fighters, Bartolomeo, Kyros, and so on.
If we placed Sanji against Zoro's opponents, even if he won(i'm still iffy in him defeating Pica, but let's say he can), he'd have won with higher level of difficulty, not only because he is much weaker than Zoro, but he doesn't have the same skillset as him to take on his opponents. Sanji may be a monster trio level fighter, but that's because they are top 3 strongest as far as the crew is concerned. It doesn't mean they are equals. He isn't even in the conversation as far as it goes with the worst generation in the overall grand scheme ever since the timeskip started.
> FI Luffy and Zoro defeated the antagonists(Hody and Decken) at the beginning of the arc in handicaped positions(in ropes, underwater). Luffy also clashed with Zoro and Sanji's end arcs opponents respectively(Hyouzou and Wadatsumi), the former who wasn't for anyone(only hired by Hody against money) when the latter was Decken's subordinate, the former gaining his respect by countering his jet pistol, poisoning him, and called "strong" by him, the latter swat aside like a fly by same jet pistol with Decken calling "useless as always".
At the end of the arc, Wadatsumi ate a single pill(that didn't even seem to affect him anymore by the end of the fight) when Hyouzou ate dozens of them, undergoing a transformation that was highlighted similarly to Luffy's opponent's.
All this to say Hyouzou was portrayed vastly superior to Wadatsumi. Sanji needed the strongest post-timeskip attack he showed yet to take him out and that was after him already be weakened by Jinbei's attack who was tag teaming with him, when Zoro defeated Monster Hyouzou with a single rengoku onigiri. So basically Sanji put more effort in a team battle against a weaker opponent than Zoro did by himself against a stronger opponent who was highlighted similarly to Luffy's opponent
> Punk Hazard, the main antagonists were Caesar, Monet and later Vergo. Sanji wasn't even put in the conversation of protagonist-antagonists battle, which were reserved for Luffy, Law and Zoro respectively. In before Sanji fought Vergo, yes he did, but he wasn't reserved for him, he was reserved for Law. That's why while clashing with him, it didn't end well for him, because he was an opponent destinated to be defeated by Law's hands. Luffy defeated Caesar. Zoro defeated Monet. Law defeated Vergo. Sanji defeated no one
> Dressrosa. Same story continues. The ones defeating the main antagonists are Luffy, Law, Zoro. Sanji clashed with Doflamingo, didn't end well for him as an opponent reserved for Luffy. Zoro also clashed with Fujitora, but he wasn't an arc antagonist. Law also clashed with Doflamingo repetedly, but he was reserved for Luffy. Pica being reserved for Zoro. Trebol being reserved for Law. Zoro received similar portrayal to Law when they defeated Pica and Vergo respectively(cutting through the full body haki of the strongest top executives while cutting through mountains)
> Zou, we have Capone who manages to capture the entire crew in a mission he wasn't even allowed to hurt Sanji and Sanji did nothing until he realized his family's name could save him and that Nekomamushi was there to help his friends escape
Now comes the cake island arc, so maybe he'd get some amount of redemption especially without Law and Zoro there, but the excuses concerning his lower portrayal comparatively to Zoro in particular with the others of the supernova trio needs to stop. It's embarassing at this point