1.) Still gives you some idea, no?
1) that was Sparing... in a Fight they'd be much faster.
2) Heavy Armour wasn't that cumbersome to Knights. Recent studies actually show they could move just as fast as a person without the extra weight, and in fact Modern Soldiers carry much more weight into Battle.
3) Do you know the speed of that Airsoft Bullet? I don't, but it's substantially slower than 200m/s. Besides, IIRC some bolts for x-bows were 100% made of metal, usually Iron. This gives it the Armour Piercing ability and the Kinetic Energy to render it lethal against armoured targets at up to 200m, whereas the Long Bow struggles to penetrate heavy armour at point blank range.
Besides Cutting an Arrow in half is different than cutting a X-bow bolt in half. For one thing, the Bow you can see being drawn, you can see the person taking aim, and then the release and snap of the string. With the X-bow you can only see the aim being taken, and hear the thwap of the release.
2.) Interesting, but does it have an impact on the use of weaponry? Like the armor being cumbersome and getting in the way a bit and the weight...
3.) Yes, its a bit slower, 400–550 ft/s (120–170 m/s), this is the average speed shot from the rifle type of Airsoft gun, still pretty fast though.
4.) Its bigger than the pellet for one and the narrator said it would be hard to see the pellet and the guy managed to cut it, the arrow is way bigger and you can still see it somewhat even so more than the pellet, it'd be harder at that slightly higher speed but the extra size should help. And don't the whistling of the bolt help detect where it would be as well the thwap?