Go Low,
It’s more than possible to hold shaft flex well beyond impact. I can do it… and Arnie posted that sequence a page or so back.
It’s a reality. It can be done, and I can do it. Not impossible. Your experts are not correct in their assumptions about the impossibility of doing it. They are wrong.
Feel free to stay in your opinion that it can’t be done… but it can. I live in that truth. Of course anyone can choose not to believe it… but I won’t be told it can’t be done. I know better.
Perimeter weighted irons don’t give accurate feedback. They don’t, and people suffer over time and slow their own progress with a lack of feedback. You need feedback to learn. That’s how we have evolved as humans. Trial and error. We need to feel the error. Without it, the brain simply can’t make the adjustments to do better next time. It’s just fact.
Modern coaches, unless they are great players themselves, much of what they teach or believe is based upon speculation. If you can’t do it yourself, you can’t possibly know what you don’t know. This is one reason I don’t teach Moe Norman’s technique. I can speculate, and probably better than most, but I would not kid myself into thinking I could really know all the inner intricacies of Moe’s approach. Then again, I haven’t really spent time trying it. I want to be able to answer every single question a student can through at me, properly. I want to be able to demonstrate, explain, and support it with fact, not speculation.
Modern touring pros are playing with training wheels on their clubs. Are they really great golfers? I don’t know. Maybe, maybe not. The would need to beat me first with a set of blades, persimmons and on a real golf course. If they can, then there is probably not a lot I can teach them. They can teach me… and I will listen… but until then… “for me” it’s an unknown.
There was a good college player that came to me last year, and we went and played a round. He had all the latest stuff… but I beat him with 50 year old clubs. Guess what? He listened. So I disagree with you that younger players will not listen. They will, especially when you beat them with antique golf gear. I worked with him, and I think he will play much better this year.
Most new golf courses are not as good, because they don’t require the full spectrum of golf shots. The fairways are too wide and flat, and the greens are too big which both require less precision to land the approach. Not much to argue really. On a subjective level, I find most aesthetically lacking charm and character.
I am sure you miss wrote the above, because surely “the mental thought” of increasing acceleration is possible post impact. Here at ABS we use the word “intention” a lot.
Flat lie angles? Unless you have played 6 degrees down, and learned the proper biomechanical methodology to do so… you simply cannot know. Speculate? yes… but not know.
Could the worlds best players, instructors and clubmakers all be ignorant?
OF COURSE! 
That’s why ABS is here.
The greatest ball striker hands down of all time played flatter gear than I do… was he wrong? Of course not.
Think about it.
Now regarding the openness of this forum? Absolutely. We always have new readers, and although many of these debates are rehashed and buried in the pages of the LTLGM thread… it is never bad to go over them again. It helps me as an instructor to re think things and I like my new tricycle analogy today. It seems correct. You are still pedaling and going somewhere… but it’s different. Just because you can ride a trike, does not mean you can ride a bike. Maybe, but not necessarily.