Stats don't do justice to this comparison, especially when you consider the 5 year age gap.
You had to watch both bowl to realize Amir was a level above Junaid.
Junaid is a good persistent bowler who doesn't possess much skill. He is pretty much like Siddle.
Amir had Wasim level skill with the ball and the knack of bowling magical deliveries.
He was a once in a generation bowler while Junaid is a very good bowler.