About the speed-shooting video
Lars Andersen is not a professional historian or researcher, He is artist (painter) and trick-shooter who has very good skills. Some of his opinions about the history of archery might be too far-reaching, but nobody denies that he has very good skills in speed-shooting.
Apparently he started to experiment with speed-shooting techniques some ten years ago, and later on he started to make videos to show how the speed-shooting works in practice. The first YouTube I have seen was released around 2012. At that time there was some debunking videos trying to explain that the video was edited, but they went quiet very fast when other archers started to make similar speed-shooting videos.
About the debunking video
There are some things which might be either misunderstood or deliberately misrepresented in the debunking video. Apparently they just watched the latest YouTube video, and did not bother to check out what has happened before. Some of the "revelations" on this debunking video were actually explained in the 2012 video.
From the context, I would assume that the debunkers have not bothered to read the book "Saracen Archery, and English version and exposition of a Mameluke work on archery (ca. A.D. 136
, With Introduction, Glossary and Illustration (1970)". Lars Andersen mentions this book as his source of inspiration in the 2012 video.
The speed-shooting is mentioned in Chapter 25 "Miscellaneous techniques and devices", Comment section 5 "Dexterity and Rate of Shooting", page 142. The section stars as:
"In terms intelligible to the modern reader the standard of rapidity the author sets for the archer is the ability to discharge 3 arrows in about one and a half seconds."
In the debunking video, the last "question" was how the 1.5 seconds was measured. Unfortunately I don't have access to the original text (which was apparently very difficult to translate), but one way of measuring this kind of speed events was to drop a scarf from shoulder level, and launching three arrows before the scarf hits the ground.
In conclusion
Sorry about this long rant.
You should always be slightly skeptical about what you read, including what I just wrote.
However, you should also be slightly skeptical about the skeptic revelations.
PS: You can find a PDF version of the book by Googling for "Saracen Archery". I rather enjoyed reading the book, and there was a lot of material which was totally unknown to me. For example, Chapter 26 "On shooting with an arrow-guide (Mijrat)" shows the devices used to launch short arrows (something like crossbow bolts) using a normal bow.
Edit. Damn... my Freudian slips are getting through the spell checker. Thank you, crodio.