It is precisely a sense of proportion that's being discussed, ask about most other bike parts and you'll get balanced responses. But pedals, and skinny tyres, seem to be in a world of their own. Everything will be so much better, you'll be faster and you'll enjoy your cycling much more, it's not a little difference it's like night and day. To be frank, as opposed to being Pussy Potsy's Patsy, I call bullshit on that, not the idea that there's a difference but that it is as marked, and as one sided, as claims make out. I also call bullshit on the idea that anyone not slurping the coolade is just doing it wrong.
Show me some real world data that supports these outrageous claims. Let me see the stats showing number of clipless moments versus number of injuries/deaths via clipless moments. Produce the evidence for the terrible dangers faced by feet slipping on flat pedals. Get some average cyclists and produce their stats with/without clipless pedals and with varying tyre sizes. Measure the size of their smiles after each ride to judge their happiness quotient.
One of the frequent arguments is that the pros use these systems and they wouldn't use something that didn't work. That's quite correct but your average cyclist is so far removed from pro level that comparisons are laughable. If it makes a 10% difference to a pro then your average cyclist would be unlikely to see as much as a 1% difference. Another argument is for safety, your feet don't slip, well plenty of people manage flat pedals without feet slipping, they ride accordingly. That's without accounting for the fact that clipless moments are expected and are not always the 'hilarious' incidents you could be led to believe.
This isn't myth busting, it's discussing the pros and cons of bike parts and should be treated the same as you would all the other bike parts, with a rational look at what you actually get.