Based on ?
I mean I have Zoro beating Kid myself but I'm open to change that depending on feats.
I think the calamity battle is very clearly being set up like Enies Lobby where Sanji beats the #3 and Zoro beats the #2, but Sanji wins his fight easier than Zoro (he's clearly going to clap Queen when the raid suit comes out).
So Oda is trying to portray Zoro and Sanji as relative.
Meanwhile, I think Zoro's feats on the rooftop were
significantly better than Kidd's.
So it stands to reason that Sanji is above Kidd as well.