Philosopher, I disagree sharply – many people can be rational and have functional lives, but live in emotional pain. Anxiety, OCD, bipolar, and much more are real conditions – perhaps calling it illness is too much; it’s more like maintaining and optimizing mental health. Ask any mashgiach in a yeshiva about emotional pain and mental health, and they will never mach avek what people are feeling. It’s callous, insensitive, and insulting to tell people to just “grow up” and stop being tortured by their conditions.
It could be that in previous times, people didn’t have enough free time to develop these issues…batalah mayviah lidei shigayon, but the way to deal with it is through hishtadlus, like anything else, and as conventional wisdom goes, keeping busy is a very big part of it, but definitely not the whole thing