FDR - the problem with people with your level of education and depth of knowledge is that you often see what is meant to be a simple statement as an affront to accuracy because it isn't supported by pages of proof.
If I had wanted to offer a cogent argument to ACs post with supporting evidence and referencing, I would have done so - but I didn't - this, as you know, has been (another) thread about VRS and SWP following yet another avoidable accident and the more off-topic the thread goes, the less value it is to those young drivers.
I have taught those young drivers for nearly 40 years in a variety of roles and never once have I been asked for mathematical proof for what I have demonstrated or explained because for 99.9% of the time it is irrelevant.
If my operational and instructional experience and credentials aren't enough for you then I apologise - I have never claimed to be an aerodynamicist nor a maths or engineering guru - I am just a fairly well trained and tested pilot and instructor who seems to have got the message across reasonably well in the past.
If you want to explain the subtleties of flapping here then please do so in language clear and unambiguous to me and those young drivers but it might be worth a new thread.
I am always very happy to be educated - I have read a number of those sources you quote and regularly refer to my Prouty and Gessow and Myers .