It is very useful in some cases - but sometimes it is the individual relationship that does the most healing. So - it is up to the person and their therapist to decide when and how long a person would find group therapy useful. However, they should also be in individual therapy, I think, to gain insight and work through problems and learn strategies to deal with their intense anxiety, mood swings, and often rage. Group therapy, however, helps them see themselves the way others see them and offer them insight into themselves they would not ordinarily get. No - I wouldn't say it has been fully discredited.
Some people have good success with it.
However, I don't know of anyone who uses it and most traditional and academic therapists don't tend to use it. However, that doesn't mean its wrong - and I don't think its harmful. It used to be thought that hypnotherapy was ridiculous. I think, in part - it is economics. Cognitive therapy has been around for 30-40 years.