Their "tests" are basically worthless other than to give anecdotal info. All three rifles had different muzzle devices (It looks like the 91 and M14 just had flash hiders). I'm sure the SCAR is lighter recoiling, but just how much lighter really remains to be seen.
They should at least fire them using the same muzzle device. I wonder if the same ammo was used?
EDIT: Apologies to the OP, I didn't realize the video was actually your own. I would have tempered my response somewhat. You obviously have access to some great kit.