I think it really started around the end of Dressrosa and start of Whole Cake Island.
Sanji clashed with Doflamingo, who acknowledged his strength, had his moment initiating hostilities against the Big Mom Pirates, led the "Twirlyhats", and then had his moments on WCI, including dodging Katakuri, clashing with Big Mom, blitzing Oven and generally just getting a lot of attention and development for future setup.
It's complete fucking bullshit Zoro couldn't get a fraction of this in Wano.
Sanji clashed with Doflamingo, who acknowledged his strength, had his moment initiating hostilities against the Big Mom Pirates, led the "Twirlyhats", and then had his moments on WCI, including dodging Katakuri, clashing with Big Mom, blitzing Oven and generally just getting a lot of attention and development for future setup.
It's complete fucking bullshit Zoro couldn't get a fraction of this in Wano.
Eos sanji aint doing what zoro did on wano.

WSS evenly matched with a cook that don't train like that and doesn't even have CoC yet.