I once heard a clinical psychologist say that in practice most of his time is not spent trying to cure mental illness but instead helping people with life problems. This seems to fit in with purposes 2 and 3 that you listed above.

As far as purpose 1 goes in my own experience we seem to be nowhere near having a cure for any mental illness. As you pointed out medicine and therapy can help with some disorders but usually people will still suffer from episodes throughout their life.

I think the mental life of individuals is poorly understood from a biological and even moral standpoint. For example, when dealing with repugnant intrusive thoughts people with OCD are taught that they are not choosing to have these thoughts and therefore in some sense are not responsible for them. However, for many people internally it feels as if they are choosing to think these terrible thoughts.

If you asked a normal person about having a normal thought such as "I am going to go eat lunch now" the person would most likely think they are choosing this thought because it agrees with the fact that they are hungry.

I have asked several psychologists about this distinction in thinking and they have essential told me that we don't know how this works. There seems to me many philosophical questions that arise about the nature of thought that arise here that are not well understood.