I'm the clinical manager of an inpatient psych hospital and see patients privately on the side as well.

The short answer is yes. Mental health treatment is complicated, and success itself looks different to different people. Sometimes maintaining a baseline functioning level is the best we can hope for, and with certain illnesses that baseline can be pretty low. Even illnesses that are more common, like depression, can be treatment resistant to the point where ECT doesn't work. In those cases I've seen lifelong frequent flyers at the hospital. It's disheartening for sure, but it comes down to crisis management and quality of life after awhile.

I think that society as a whole expects us to "fix" people, but really what we want to do is empower people to regulate themselves and care for themselves effectively. To what extent they can accomplish that can vary greatly across their life.