The ufopedia mentions knocking someone's gun away, rather than grabbing it and the illustration, even if it is from a very silly movie, brings that point across nicely. The way, that cqc plays out on the battlescape also looks much more like just knocking the gun away. You don't need any strength at all to mess up somebody's aim. It is surpisingly easy to miss a man-sized target even from point-blank range. The defender only needs to be faster than the shooter and give the weapon a slight push. Of course the game is totally exaggerating, when it shows the shooter spinning around up to 180 degrees. I understand, that the mechanic has to be visually communicated to the player somehow but that is a bit much.
Anyway, grabbing an enemy or their weapon makes a lot less sense to me from a gameplay perspective. Why would the defender let go between every shot? The attacker would first have to free himself before being able to take aim again. Also none of this would even be possible to begin with, if the defender doesn't have a free hand.
I guess it could be cool to have grappling and even disarming mechanics in the game, but the amount of complexity we have already is sufficient for me.