Let me see if I can sum it up.
O-sensei saw and trained some Kashima Shinto Ryu katas through his son K. Ueshiba who was taught these by instructors of this school.
He probably saw and experienced other schools sword and weapon katas as well. It's e.g. reported that O-sensei practiced with a student within one of the Kuki shin schools. I bet it didn't end there. Remember there is a great deal of weapon work in Daito ryu. O-sensei was probably interested in budo enough to visit and watch many sword schools, even if he didn't practice there.
O-sensei more than most was a man who took his own budo development and practice more seriously than his teaching. During the Iwama years O-sensei would practice and experiment with the jo and sword and of curse the things he had seen and trained would color his own creations. Since he needed a partner for many of the weapon practice Saito was available.
So the weapon practiced today within the aikido community - that comes from O-sensei - containes stuff that look very close to old koryu katas (e.g. some kumi jo and kumi tachi, not to mention the old kata Ki musubi no tachi) and other stuff that look far from koryu weapon work (e.g. some ken and jo suburi).
He didn't try to do KSR or other Koryu school weapon. He just tried to improve his own budo (aikido), and so trained day out and day in with the stuff he had experienced and the creations of his own.
This is at least how I see it from the various stories and interviews that is out there.