Funny thing for me is, i can cum with a 50-70% erection.
As for all you wrote, i tried it before and never got any improvement.
Im pending on getting my frenulum surgery done, will update my thread after I get it done and it heals, will report again and hopefully I can last longer (it's a bit too tense).
I have done the same (came with 50-70% erection). When I would do that I would put a tremendous amount of tension on my PC muscle and I would not be breathing correctly, if at all, and I would "crunch" my abs and lean over slightly (or I would be sitting in a chair, leaning back quite a bit). All of that combined caused me to ejaculate extremely quick. Embarrassingly quick.
As for the surgery. It is your body. You can do whatever you want to it. When it comes to surgery, I think that should be an absolute last step.
Back when I was not too great at controlling my excitement I was completely unaware of the behaviors I was performing which caused me to ejaculate so soon. In no particular order, here they are:
1) Involuntary kegels (basically telling my body I need to ejaculate)
2) Holding breath (this traps tension in your body)
3) "Curling" pelvis forward (traps tension in PC muscle and groin/lower glutes)
4) "Flexing" lower abs (traps tension in PC muscle)
5) Thinking about ejaculating too soon (your brain cannot think in opposites; this was stated in the OP)
6) Tightening legs, locking my knees (traps tension in PC/groin/glutes)
7) Eating too many simple carbs (sugary foods/drinks increase the likelihood of PreE)
8) Being nervous/negative (I was harsh on myself, put myself down, thought no woman would want to be with me, etc)
There are probably more I have discovered, but I just can't remember them right now. I had to practice controlling the above behaviors before I could last long during sex. It was tough, frustrating even. However, after I figure it out and I was willing to dedicate myself, I saw significant improvements in two weeks; even better improvements after four weeks.
If you truly know you have done everything in your power to understand your body and you still cannot control your ejaculatory response, then your next step is completely up to you. I am not going to tell you what you can and cannot do. I will tell you that I thought I tried everything then I sat down, evaluated my dedication and my understanding, and I discovered that I really had not tried all that much and I was just feeling sorry for myself and my premature ejaculation. After I got over it, I saw progress.
Good luck with whatever you choose.