Like I said earlier, it's an interesting clip, lots of humor in it... However, since you insist, its conclusion goes in the opposite direction of everything I have learned about swimming over the last 25 years, both as a swim instructor and a swim coach.
Some good can be said about the clip, the ideas that it promotes are not fallacious, it's just the result of the process which I humbly believe which is (fallacious).
You couldn't get me to perform this exercise, not to mention my heaviest sinkers, who have a negative buoyancy anyway (that is, they can not even float with lungs full of air in a perfectly vertical position).
I definitely stand to be corrected, always eager to learn, but you'll have to provide me with evidence that this works, evidence in the form of videclips of *you* getting a typical heavy sinker to float in a perfectly horizontal position without the help of any aids, and no movement at all. Read in this request that I even suspect the author of this clip to have cheated, I don't know how (either in displaying the few times when this trick worked whilst hiding all occurrences when it did not work, or by altering the clip in some ways). The proof is in the pudding. Show me something valid, and I'll buy it no problem.
The story I posted, which you commented negatively, was done with a lot of honnesty. It depicts an actual 90min session during which, the subject did go from being able to swim 100m non stop, to 2000m non stop. It means that prior the 90m session, he couldn't swim, after the 90min session, he went to the public swim session and booked 2k non stop. The same subject just did his first 2 triathlon races, he's now eager to hear the Horn at the start of his next Ironman race. There's not cheating in this clip, and more importantly its conclusion is inclusive, ie it pertains to everyone having this problem without a single exception.
I'm sure that all coaches with significant experience have all been confronted to very heavy sinkers, we all know that for a large portion of them, floating still in a perfectly horizontal position is physically impossible. Your clip sends the message that everyone with no exception should manage to float, which is very frustrating for those who will never be able to float this way. In that, it's exclusive (and once again, based on my experience, fallacious).
"Some would rather be known, than be right" (Andrew Coggan, 2011)
Charles G. Couturier, Canadian Swimming / Triathlon Coach