I'm not quite sure what your getting at here?...Two of the advantages of aluminium rads are that they don't use solder for attaching end tanks(which is a poor conductor of heat) and they last longer than copper rads.........Like all things in modern cars... The switch over to Aluminum was based on cost and weight.
There is no denying that aluminum weighs less. The weight savings contribute to epa/dot - fuel economy, weight classifications, etc. But remember, most aluminum radiators are fitted with plastic tanks too. Every wonder why Aluminum radiators are replaced, not rebuilt? Just a thought?
Most things I have read don't dispute that copper dissapates heat better than aluminium but the overall design of the aluminium radiator is much better and more effecient than the copper rads.
Here is some good reading..Just ignore the first column regarding the corvette stuff.
DeWitts - Why Aluminum