I don't quite get the premise of Fisher's observation. Andy Murray is a total package. He comes with his attitude. You cannot separate him from his attitude. For me it is almost like saying " we don't know how good Murray would be if he had a better second serve" . Attitude is as important as a second serve. So, we KNOW how good Murray can be: THIS is it. If he changes certain things in the future, then we will know how good THAT Murray can be too.
clap