In my 35 years of watching the Cubs and 25 of which was fervently, I can say without a doubt that he has the best arm we've ever had out there. And to think that he is ALSO the greatest defender we've ever had in CF is crazy. The speed guys rarely have a cannon, you might see some flashes. With PCA it's like every time he is tested he has a legitimate shot to snuff the attempt.
Base hits up the middle with a runner on 2B used to be damn near automatic runs.
Btw, his arm is another big whiff by the scouting community.