Sanji led the crew throughout all of Dressrosa to the point where the crew was called the Twirly Hair Pirates
Now obviously Zoro is the VC and more important in terms of leadership but usually Luffy is there so Zoro isn't doing much on that aspect other than fighting except scolding and keeping Luffy in check several times. That's why I feel Sanji is more important outside of fighting since he covers up for it with cooking and can be a good leader too
But yeah, Zoro is so many dimensions ahead in terms of fighting that they're both important and since Zoro is the better leader, he's the #2.
Point is Sanji isn't some bum with no focus, WCI wouldn't have happened otherwise