Once again you astound me with the hard cold truth.
Where were you when I was younger and desperately needed this advice. My band had a deal at Warner Bros. in the late 90s through the early 2000s. We lost our manager just as our single was about to be released to radio over some dumb internal shit that could have been avoided. Our manager felt slighted over a money issue and my band was too prideful and self righteous to go back and make it right with him. What made it worse was our then up and coming lawyer fueled the fire against our manager and made us feel justified in not taking the high road and making peace. It was terrible advice by someone who should have known better, which is ironic considering our attorney at the time is now the manager of the _____ _______.
Shortly after our attorney abandoned us and no one wanted to manage us because any serious billable money had already come from our record advance and publishing deal which was long paid out and spent. Back then without a manager to advocate and fight for you at a major you were dead in the water. Especially if you were one of those "developing" acts on the label which we were. What people don't realize who haven't been on the inside of this scenario is that you don't just have to appease your A & R guy and his boss, they're generally already on your side because they put they're asses on the line to sign you. You have to appeal to every single department at the label that matters to your career including marketing, PR, distribution, radio promotions among others. Each one of these departments have their own agendas and pet projects. You have to have someone to rally all of those departments around you to support you at the right moment, timing is everything and without a manager this is nearly impossible.
Long story short losing our manager killed our single for the most part. It was a mediocre success at best even with a video (back then MTV still played music). The single actually did more to help the act we'd collaborated with than us. Our record deal (which was starting to look up) lost steam and we fizzled. We managed to hang on for another year or so by the skin of our teeth but it was a slow painful decline that I will never forget.
That last year was made up of me trying to desperately find a manager and save our careers while my band unraveled, it was like grasping sand. I regret not making peace with our manager when I had the chance, it might have changed our outcome significantly. It was not just a bad decision but a career killing one for me as an artist.
Since then I've had a few minor successes, a few Billboard top 10 singles or remixes as an indie producer / writer / DJ (Mostly on the Billboard dance charts) but I'm getting older now, I'm no longer on the cutting edge and I kinda had my big break and f'd it up. To some extent I've reinvented myself and make a living working in the industry but my big break to make it as a young up and coming act is gone forever.
Maybe John Mayer, since he's still practically a household name, can do better than a developing act like ours did, but like you said he's getting older too and so is his core audience, age isn't your friend in this industry for most artists (there are few exceptions).
Anyway the point of my story is to warn younger artists to not be cavalier about their relationship with their manager. If they are lucky enough to have a manager that is loyal, hard working and honest, even if things aren't always going your way, hold on to them and foster that relationship. A great manager will make or break a band. A manager who is loyal grows with a band and keeps its dirty secrets while constantly advocating for you and navigating the complicated web of people that have to be appeased in order for you to have a shot.
Young bands may not understand that just having a good song or being the flavor of the month isn't usually enough, the business and political side is just as important and this is why a good manager is so crucial.
Mikael Johnston