Gaban doesn't need to be a perfect parallel of Sanji for Gaban gas to be Sanji gas
It's about the fact that third strongest of the crew won't end up weaker than the third strongest of Roger's crew (Oden is kind of an exception as he joined very late in Roger journye) because straw hats are clearly going to surpass them.
Gaban is basically Sanji floor level
 
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