Do you think women would write about their experience if they felt they had "failed" at hypnobirthing? I think they are much more likely to write, singing it's praises. Who knows, these women may have coped very well anyway?
Going on my NCT experience again, I know of several women who have done hypnobirthing training plus the NCT coures. They say that NCT were far more realistic and that hypnobirthing was a waste of their money.

Purely anecdotal, but it does make me question the training.