Isnt a normal fishman 10x a human in dura? The king of the sea is probably more durable than that +King dura+ devil fruit, Sanji needs to go super sayan to beat flame on jimbe.
It'd be a base normal human compared to a base normal fishman. It's not like arlong is 10× more durable than current sanji.
And sanjis had bodily modifications. He's not a normal human anyway.
Sanji would need one anti manner kick course to stomp a hole through jimbeis fat ass forehead