I don't know that you could say the new alloy FE heads "don't flow that well", perhaps you could say the old iron heads were pretty darn good!
Of course the alloy heads offer a major weight reduction and Edelbrock and Shelby are the only modern alloy heads I'm aware of for the FE. Cam profiles are about as scienctific as it gets, very complex stuff. Thats why it's difficult to reach a conclusion on the matter without hard numbers. Which in the case of the FE are simply not available, like the data is for so many other "typical" modern motors.