He also educated the entire industry on how it works. Most people today show off that they're a security consultant but they haven't really had any experience breaking into things, and a lot of the advice is impractical. Like everyone knows that MD5 is insecure, but who's going to actually use it as an attack vector? Mitnick does the attack and then documents it. Some people claim he made stuff up, but even having the kind of imagination to make up these scenarios puts him above many security experts.