Sure copper provides more conduction than aluminum, but we aren't using much conduction unless your brew pots are several inches thick. The convective heat transfer is what is happening between the air and the pot, and the pot and the wort. What we're seeing is natural convection on both sides, unless you're blowing a fan or stirring your wort which obviously increases the convection. I believe this would make Aluminum much less efficient than you said in the podcast (about half as efficient) due to the fact that it has a higher (Reynolds number to Thermal Conductivity) Ratio than copper.