I've seen plenty of techniques demonstrated with an armed nage. All sorts of ushiro variations that make no sense at all unless nage has some sort of weapon. I don't think you have a good point here.
I won't discount the value of aikido in weapons retention but Chris asserts that the reason the wrist grab even exists in aikido is to prevent an armed nage from attacking uke, which is really backward.
But who have you seen demonstrating these methods and can you post some link? Also, please describe anything in aikido unarmed technique that only makes sense if understood as involving weapons?
Extra points if it's O Sensei or one of his major deshi.
Best to you.