A more myopic view point there could not be.
As long as people hold weapons (any and all weapons) in their hands, Aikido's techniques are valid. Whether it's a club, knife, screwdriver, pistol, rifle, stun gun, laser blaster, or sonic disrupter. If you or they are holding it, Aikido has an answer.
My point is a self defense art should not fall apart when your attacker is unarmed. That makes it woefully lacking as a self defense art.
Ahh he only has a knife, piece of cake. Oh no! He dropped the knife, now I"m screwed!