With all due respect, that girl just walked along with him. That was not a wrist attack, he held her wrist and walked her away. The girl in the video made no attempt to resist. I don't see how this helps your argument.
His first step was to approach her. Then he grabbed her wrist. I understand he showed her a knife and it scared her so badly that she didn't resist even after he put the knife away.
But the fact is that his primary attack was a wrist grab. And the attacker
had the knife. Not the defender.
But let's go further. Can you show me one
example of O Sensei's having a knife or sword against an unarmed attacker?
I don't think so.
I know that I have seen countless examples of O Sensei unarmed
facing 1) sword; 2) knife; 3) multiple attackers.
I've also seen O Sensei with a sword when and only when
1) he was alone; 2) when the attacker also had a sword or spear.
I've seen O Sensei demonstrate 1) sword against sword; 2) jo against sword; 3) fan against sword (and maybe fan against spear or juken).
But I've never seen O Sensei demonstrate armed
against un unarmed attacker (except possibly fan against unarmed). Mostly, it's O Sensei unarmed against sword or unarmed opponents.
So to lend any validity to your claim, you need to show at least one example of O Sensei's using a knife or sword against an unarmed attacker.
As to a theoretical koryu link to aikido's reason for practicing against a wrist grab, I'd have to ask you to be specific and explain where the link is.
I'd say that Mochizuki Sensei probably had more technical koryu and general weapons experience than any student of Morihei Ueshiba except his old pal Yoshio Sugino. They both trained extensively in katori shinto ryu and both continued this throughout their lives. I trained thousands of hours in Mochizuki Sensei's form of TSKSR and saw his relation of sword and other weapons to aikido. Of course, this was not O Sensei's method of sword, which was not koryu but his own development; but, as much as Mochizuki Sensei related aikido to sword, he never put any emphasis on grabbing a swordsman's arm to prevent his drawing the sword. It seems that that little explanation is a very tenuous attempt to link modern aikido to the samurai.
It has about as much relevance as trying to explain our love of pizza as a vestige of having once had gills, when our ancestors supposedly lived in the ocean.
I think your aikido will improve quite a bit when you let go of that theoritical imagination and start dealing with human life in the real world.