I'm inclined to call fraud on many of the claims in the video .
To begin with , the quality of both the mail and warhead is not only unmentioned but unverifiable too .
The mail could have been made of plastic for all we know and palming something as small as that busted link He showed {which burst on the wire its' self , not the rivet which is highly suspect to my mind} is pretty easy to learn .
Also , the maile is without padding and laid flat on a rigid surface {which for penetration is cheating shamefully !} .
Not to mention , the video shows a pyramidal shaped bodkin and claims it was for armour piercing when from what I have read , all the examples found of such heads were too soft for such and would have been for flight arrows instead .
Second , there is no way He is pulling any useful draw weight with many of the arm positions He uses .
The Human body is a machine and there are limits to what it can do in what fashion . He is using a very weak grip on the string/arrow and is pushing the bow forward using what would be a very weak jab in boxing .
Regardless of how much strength work He might have done , that bow would have to be pretty anemic .
It would have been worthless in battle unless the enemy were unarmed rabbits .
Third , I would like to know where it is recorded when Saracen archers were tested and had to be able to shoot 3 arrows in 1.5 seconds .
I would also like to know when Medieval Arabs started measuring passages of time in fractions of a second .
If the time span was a heartbeat , the ability to stop ones own heart beat is fairly common and is taught to high level competition shooters and so easy to learn I taught Myself to do it as a teenager {it sounded like a cool thing to try at the time} .
It is quite plausible that a shooter might be encouraged to master the ability to shoot between heartbeats {the pulse of blood through the body can disturb aim} and being able to hold off the next beat for three shots might have been something of a self measured standard {or more likely some sort of poetic expression which is common in Medieval Arabic} , though I have never heard of it before .
It is possible to hold of the hearts' next beat for more than 1.5 seconds with practice .
Finally , the whole video just plain sets off My B.S. detector .
Edit : I mean no slight on you Jurgen , the harshness is directed at the people in the video .
This video
https://www.youtube.com/watch?v=2yorHswhzrU seems more realistic to Me , but also illustrates your question {how can this be modeled in G.U.R.P.S} .