You cannot compare the raw thermal conductivity of a fluid like air (that pulls heat via convection) to a solid material like plastic (that pulls heat via conduction). Especially when the fluid is being actively moved with the intention of cooling down the plastic.
On top of that, the lattice structure of the infill will mean that heat will not conduct away from the channels well regardless of the material used.
On top of that, the lattice structure of the infill will mean that heat will not conduct away from the channels well regardless of the material used.