Considering the fact you've come with a far more reasoned approach than OP, I'm going to bite and ask if you agree with a couple of statements and if you can compile any specifically useful evidence.
For starters, let's take your proposal that this exact 6% brake boost technique is the most effective version (and is real) to be true - would you agree that a) this is too precise for a human to reliably pull off in a live race situation, regardless of how alien they may be in skill and b) there's no application for your wider threshold "15-20% with short gears" technique in sport mode due to fixed setups and the lack of grid starts in general?
I'm willing to entertain some lesser known quirk of the physics that only really rears its head in the relatively obscure world of drag, but I'm far more reluctant to accept that this knowledge is widespread among some gatekept community of fast sport mode players. It smells too much like a convenient belief to avoid accepting that people really are that good on merit.
I'd be very intrigued to see meaningful evidence of either the manual technique or the supposed script (which I don't see how you'd reliably implement in a racing game) can produce a fast lap (let's say, within 1.5% of the top lap on a Friday, a fair control for a high rates frequent player IMO) in an active qualifying session for an active daily race, in a bopped settings locked gr3 or 4 car. I'd reason anything short of that is not sufficient evidence to suggest this glitch, whether well known in the drag community or not, has any influence on the landscape of the playerbase in sport mode.