I think YABU OP.
What you just quoted - my body will open up easily - is an affirmation. If explained properly, its main purpose is to convince women that their bodies are capable of labour. It's amazing how many women- myself included- have no real sense of what dilating to 10cm looks like and are freaked out at the idea their bodies can't manage labour. For lots of those women even if they're capable of an intervention free labour the fear can lead to panic and shutting down.
I had an epidural, back to back, failed induction, ventouse. The hypno birthing course I went on was called gentlebirth and it was all about using the tools for any labour. It talked through different scenarios, there were recordings for a positive induction and a positive c section. It and a tens machine got me through the 18 hours before they let me have an epidural.
A good friend has had four children and genuinely swears her last two labours she experienced as largely pain free. The first two were positive experiences, she was induced on the first. She reckons she essentially self-hypnotised using yoga breathing which got her through all of them.
I think it's fair to say there's a percentage of women who will always need intervention, a percentage who are very likely to have an easy birth, and a big chunk of women in the middle where their experience - the support they're offered, the interventions suggested, and yes how much they feel in control- will have an influence on how their birth goes. The challenge is nobody knows in advance what group they're in.
I think hypnobirthing can help women who feel their bodies won't be able to go through childbirth in feeling in control of the process. It's not a magic bulllet. But social media will find anything to make people feel part of clubs/behave like idiots. I didn't feel like a failure, I felt like a superhero even though not a single part of my birth plan came to pass.
I think idiots on social media and people putting pressure on themselves can't be blamed on a method. Courses that present unrealistic ideas is a separate issue from whether hypnobirthing is a useful tool.