OK. So I'll go there as we've already run this thread off the rails. And that it's a fun topic at a time when not much else is going on and it's burger flipping season.
I'll chalk this up to the ole "you can find anything on the internet" saying and possibly the age old adage about stats.
Kenji is a well known chef and knows the science.
However I've done the same testing. I did it because I like to win competitions.
We came up with very different results. Now mind you, I almost never cook burgers in a pan or on a griddle unless I'm doing smash burgers. Most competitions tend to work with more than just burgers. So most of it is done on a BBQ.
I've never tested it on a solid surface. It does make sense that on a griddle or in a pan, there is nowhere for the juices (aside from water) to go. So it probably matters far less than if you are running them on a grill, or a BBQ (open flame). You will retain more fats on a flat surface.
You'll find that there is equal debate as to which has better flavor between a griddle and a broiler. I like a good greasy burger quite a lot. But I enjoy a broiled or BBQ'D burger flavor better. By flipping once, you lose less fats and "juice" than if you would if you flip a bunch. You'll also generally have less flare ups as the grease doesn't end up in the flames.
I would never do a smash burger over an open flame as they would no doubt become burned up burger pieces.
So my take would probably be that if you're cooking on a solid surface, probably not much difference. If you're bbqing a bunch of burgers, I would highly recommend the one flip method.
Next up... to quarter turn or not to quarter turn.
