TBF, I really felt for you reading your OP.
First of all, what you are feeling is entirely normal and very common - we all idealise how we want our births to be, and if they deviate from that even slightly then it's easy to feel "a failure". I think these feelings are especially strong if you have had a career before the birth and so are used to being in control. I believe there is too much pressure on women to "achieve" a perfect birth, when a lot of the time the reasons for less than perfect births are not in our control (inadequate medical help, baby's size and presentation). This isn't helped by the terminology of childbirth "classes", as if it's something you can swot up for like an exam.
Secondly, you went through far more than most women do, so don't be too hard on yourself! Up to 8cm with no pain relief!!! And three hours pushing!!! Blimey, I know I couldn't do that.
Finally, just bear in mind that in Afghanistan, one in seven women dies in childbirth. The statistics were similar here before modern medicine. So accepting a bit of intervention is not "failing" or "giving in", it's just common sense to give the birth process a helping hand if that's what's needed. If you hadn't agreed to the ventouse, who knows what might have happened?
I don't want to make light of your feelings because I felt the same after my first traumatic birth, but thinking things through, and especially talking them through, will really help. It's great that you are enjoying your ds so much - it only gets better, I promise you! And your feelings about the birth will get better with time too.