I think a diagnosis is most useful when it applies to certain benefits, like ADHD or autism. Otherwise, I think the treatment is what's most important and not the label. However, if you don't think you are receiving the proper treatment I would seek out another T.

In the US, only insurance and medical providers you give permission to have access to mental health. Otherwise no one knows your diagnosis unless you choose to disclose it. If there is any concern about stigma I would not share this information.