He isn't Sanji 1:1 just like Rayleigh isn't Zoro 1:1, but they still parallel each other in their inner-crew relationships and some other traits.
Oda even introduced some fat merman that will likely be Jinbe's, but it's not like the whole crew needs a parallel, usually only Luffy and Zoro get one. It's not bad for the monster trio as a whole to have one for once.