I've done this. It mostly worked - but I had to give up some of my management responsibilities because of my health problems. I'm still gainfully employed but my superiors don't look at me as being the number one player on my team anymore- probably the number two. Another guy who spends all of his time working on weekends and on nights has taken on that role.
It's always a trade off. The organization does what it can get away with. You can pull back to 40 hours but someone else will fill the vacuum that you left behind.
So: I agree. Tell your bosses that they need to better manage client expectations, but recognize that they won't because they think they don't have to (other people are doing the work right? Management's work/life balance is fine!) You might be giving up some upward mobility or your 'irreplacable status' in your team. If you're anything like me, this will be an acceptable price to pay for you to regain some work/life balance and your health.
I think his point was to only do this temporarily while preparing to leave for another company, whereas in your situation it seems you sought to stay at your current company while maintaining a lighter workload.
Yes, that's true - and I guess my point is that you can dial it back without necessarily planning to leave, but it comes at a cost. And, better yet, the cost may not be permanent - you could regain your former status by dialling the hours back up and making sure your superiors notice, or learning how to work smart as a substitute for working hard. The other people are bound to burn out eventually.
I guess I should provide the disclaimer that a lot of this depends on your history with the company. I singlehandedly got my company through a transitional period that has caused it to double in size since. That bought me a lot of capital. And while I have not been able to keep up that pace since then, my bosses remember even if their attitude seems to be, "What have you done for me lately?"
It's always a trade off. The organization does what it can get away with. You can pull back to 40 hours but someone else will fill the vacuum that you left behind.
So: I agree. Tell your bosses that they need to better manage client expectations, but recognize that they won't because they think they don't have to (other people are doing the work right? Management's work/life balance is fine!) You might be giving up some upward mobility or your 'irreplacable status' in your team. If you're anything like me, this will be an acceptable price to pay for you to regain some work/life balance and your health.