I can't believe Byrne couldn't parlay his years as the drummer in Smashing Pumpkins into any other professional work. That fact alone speaks volumes to his performance.
Poor dude had the dream gig but simply wasn't up for the challenge. It's a well known "secret" that Byrne was a huge problem on the Oceania tour. He just wasn't able to physically handle the workload. His wrists were all fucked up and he had had a bunch of cortisone shots. It's been said that his wrists literally sounded like cement mixers.
Dude must've known the writing was on the wall after that. Can't blame Billy here. He gave the kid a chance, and he just didn't prepare enough to handle the workload.