This is a question which is hard to parse out the answer to. Doctors tend to err on the side of caution.
I've been in a position wherein I (in retrospect) believe I had maybe a bit of hypo-mania, but the depression was much worse. The doctor didn't see the depression because I covered it up due to not trusting medical professionals (at that time). She prescribed me depakote, which is a mood-stabilizer (it's kind of a fad these days as to how much they prescribe it) that works almost entirely for mania, not depression.
The result is that I became maybe a bit less anxious, but that was overwhelmed by a feeling of increased depression. I have no doubt that it's a very good medication for many, just not for me. It took me opening up a little by saying that it made things okay on the outside, but not the inside, for her to prescribe something that more targeted my symptoms.
I think most would agree that being able to listen to people, and more so, to entertain a conversation with others which partially centers on their experience, is both a sign of beneficial self-confidence and throws grandiosity into doubt. In a general sense, people who are grandiose throw themselves in the spotlight as much as they can. Importantly, though, grandiosity doesn't always feel good. There are plenty of schizophrenics who would rather not believe that they're a target of an advanced governmental operation, who would choose (given the option) that they wouldn't hear people talking about them all the time.
I think self-confidence is a tricky thing to master for people with mental health issues. They're already stigmatized by society. They may be more prone to trying less to succeed because they have an extra issue to deal with which most people don't have to face. They usually have to deal with more environmental stresses than others.