Well, I would not say a diagnosis doesn't help, because although therapy is difficult to get (although that is very common, that it takes some time until you have found the perfect match, no matter what you have).
But: At least you know, what helps and e.g. that beating social anxiety it not that much about talking about your feelings, but learning it. That you develop strategies to cope and that can be done - in my eyes - to a certain extent which "just a good psychotherapist" (someone who actually takes a book out of the shelves and is able to read, because no matter what diagnosis the patient have, if it is not one of the most common or an "out-of-the-book"-case, then there is not THE therapy and it will be adapted to the need of the patient.). [Yes, I know, in the UK it takes very long to get psychotherapy, so trying out is probably harder.] A good therapist would als say openly, that he has no experience and/or no interest (time) to take you as patient.
Thus I would say, it is more than just a label, because it gets you an idea on what you have to work to reach the state you want and as you are already diagnosed with something, thus "labelled", I don't see the argument with the label. (Depends on the others, anyway, ... it is with any illness/disability.)