Dave Mustaine was ranked the #1 all time heavy metal guitarist by Joel McIver, he fronts a band that has sold millions of albums and has sold out hundreds of concerts worldwide, he's appeared on television and in video games and even has a black belt in taekwondo. Yet he's still generally thought of as a disappointment.
Why? Because Metallica kicked him out of the band ? Please. By all measures of success, Mustaine is the definition of the word and to label him as anything but is reflective of our own failings, not his.
On the other hand, he takes a hard line born again Christian stance while playing for a band called Megadeth without seeing the irony, so maybe he deserves his lot...