By now people should understand the irony (?) that Sanji is a narrative tool and at the same time the character who got bound by narrative the most.
He is there to hype Vergo, Doffy, King, and probably others too later.
He should be able to do a lot of things that can change the direction of the story a bit, but Oda won't allow him, for example didn't notice the PH soldiers to make everyone got gassed.
It especially apparent in Wano. He can lowdiff Page One, but got ragdolled to showcase RS defense. He is fast enough to save Yasiue (see WCI speedblitz) but the plot requires him dead. Once again doing no damage to King to hype him up + RS defense. Stayed at BM place so he can't go rooftop. Can dodge all Queen's lasers beams but still got damaged by his other attacks so Exoskeleton can awaken. Even after Exo awaken and gained ultraspeed, he still got attacked by Queen so he can reasonably faint.