DF reflects the strength of the user
I've been thinking and I've concluded that the strength of logia fruits depends on the user. Not all logia fruit users can be as powerful as we've seen. Crocodile, Eneru and smoker don't only possess strong DF but also incredible combat abilities. Look at how many hits Crocodile took from luffy when one of his punches could knock out ten men?
Eneru,even weak against rubber put up a great fight. So the point is that if General Aokiji could freeze the surface of the ocean, but even with his ability neutralised like that of eneru, Aokiji is still physically stronger than luffy, theoretically.