Reality Check Time
Welcome to the site, and please understand I wasn't aiming at you, but thousands of people who contribute to the myths.
Thanks for the welcome.
I still must reiterate that what you call a myth is based on a solid engineering discipline known as "fluid dynamics". So far the only argument that you've given for your "bigger is always better" myth is a misquote that equates flow rate with tube size although that's not what was said, name-calling and
ad hominem attacks against people who you don't agree with. You may think that's a winning argument, but I don't. Quite the opposite in fact.
Your claim "no race cars use an exhaust unless required to" is false. I challenge you to show me
any racing class that has nothing at all bolted to the ehxaust ports. There are many racing classes (Indy and F1 for example) that use very complex "bundle of snakes" exhaust systems not because the rules require it, but because the carefully tuned pipes really do increase engine efficiency and power. Whether you like it or not, using pipes that flow far more than the engine can produce will gain you nothing but dead weight. And the last time I checked, dead weight makes a car slower.
In fact, equal length headers are an old and crude attempt to equalize exhaust flow that doesn't work because, as I explained before, exhaust flows in irregular pulses, not in continuous streams. (Tri-Y headers do address the pulse timing issue, but are rarely seen on road cars.) The thing that makes long tube headers work is the length of their length, not the equality of their length.
Today however, thanks to computer aided design programs, engineers can design more compact exhaust systems that can fit into increasingly cramped engine bays, and still deliver more performance gains than older, non-engineered designs. That's not a myth, that's reality.
Another one of your myths that I'd like to bust is your notion that when the ECU is in open loop mode, it's deaf dumb and blind. Not true! There are things called mass air flow (MAF) sensors, throttle position sensors (TPS) and other input devices that give the ECU plenty of information to choose optimum fuel delivery, spark and other settings (e.g. cam phasing), depending on the engine. It has been a very long time since primitive ECUs had to rely on static maps when the oxygen sensor was unavailable.
BTW, one big advantage of systems that use a MAF sensor is that they automatically tune the ECU for optimal performance if changes are made that affect air flow. Of course there limits to this, and radical changes need custom tuning. But my point is that your latest claim that "people perpetuate these myths" is not factual.
As for your claim that chassis dynos are only useful for a base tune, I must say that you have it backwards again. Are you unaware that a good chassis dyno (I'm not talking about the simple ones that's all drag racers need) essentially duplicates real world driving conditions? How do you propose to gather data on the road without a dyno? Do you think that a $300 box with a cheap accelerometer and a rudimentary algorithm to guesstimate 0-60 and 1/4 mile times is a finer instrument than a $50,000 machine full of finely calibrated sensors that don't have to guess?