If you want to see how aikido works against an opponent who is really trying to stab you, watch some Shodokan style competition.
Do you have a ref for that or a site I can watch. I have NEVER seen a competition where someone is really trying to stab someone (unless its like they do in the Philippines). I have seen plenty of DEMOS but not a competition with a knife using Aikido.
The demos are a bit obvious, even the realistic looking ones, one can see where the technique is about to happen as the decisive attack is often telegraphed deliberately (and sometimes hidden from the audience
I would never use one of the aikido knife taking techniques on a person brandishing a knife ... unless they handed that specific opportunity to me on a platter, ie. they didnt know how to attack.
I organised some knife defense/fights (outside the dojo - home training) once, with large red texta pens. The results were quiet surprising and confronting for a few people.
But then a LOT of what we do in the dojo isnt fit for the street IMO.