First up I wondered at this comment:
"At the beginning of the year, an 8th dan Hombu shihan came to my dojo in Hiroshima and taught a seminar. He was a direct student of Ueshiba Morihei and recounted his experiences of O Sensei forbidding weapons training at the Hombu Dojo....."
I often look at these comments with a jaundiced eye.
This is from 1960
I can think of any number of counters to that comment. He walked in and saw outrageous goings on and banned them. After his retirement he was known for telling students they were not doing HIS aikido. I can certainly see him walking in to hombu and seeing the shenanigans going on with "sticks in their hands" and summarily banning it. I weight that against the modern shihans comments you shared with us; something about telling some demonstration committee that "We should not do weapons in public displays, the more educated budo people will laugh at us."
Maybe the old man was just the first of the "more educated people" to see it…and he tried to stop it before it began!
Or in line with what George Ledyard has said. O'sensei felt the students of Aikido were there to enpower the Avatar (O'Sensei).
Maybe he did not want anyone else to become another avatar.