If Sanji were dedicated enough, he should have learned Rankyaku which is actually useful for his arsenal. Soru, Kamie, Tekkai, and Geppo pretty much Sanji can do. Finger pistol obviously not for Sanji but Robin should have get that.
Where another variant of Sky Walk (Blue Walk)?
Where superior Soru (invisible speed)?
Where superior Tekkai?
Where superior Kamie?
Oh wait, only Sanji has all these.