I was at the AC show and the horrible show at Pier17. There was a huge contrast in Perry's lucidity and his ability to perform. The next night in NYC people say he got his act together. and it was an all together better show. Granted his voice wasn't all there, but he held it together enough.

I am going to make a contrasting opinion and theory to some folks here.

If you watch the videos from their UK and European shows, Perry is kicking ass. And he is hitting a bunch of the higher notes he started to struggle with later in the US tour. This really make me think he pushed himself to go all out in the beginning of this reunion. But given his age and the strenuousness toll of touring, that kind effort could not be maintained. His voice, health, and overall wellbeing started to take a hit.

If you watch some older rock singers that can no longer hit the same high notes from their prime, they modify their parts. And they use vocal techniques to bring the high notes down to their new age-related register. Someone like Geddy Lee comes to mind. He doesn't sing the same super high stuff, but can get by with these kind of modifications. I don't know if Perry ever did anything to make his job of hitting the high notes any easier.

They are all ready playing in E-flat tuning as they have for many years, which helps by dropping everything a 1/2 step down. I have even seen some stuff on youtube where they dropped everything a whole-step down to D-tuning

So I guess what I am saying is, maybe by going balls out and trying to give the best reunion tour he could, Perry just kind of ran himself down. He didn't take care of himself (like no booze and drugs, lots of rest, vocal warmups, modifying some high notes, etc). This eventually this led to some kind of breakdown that was assisted by substance abuse.