Re: Horikawa teaching Shioda?
It seems that a number of Ueshiba's pre-WWII students had aiki to various degrees. What they may not have had, was a cogent method for teaching it, other than hands-on transmission.
Perhaps that is where the real issues arose - the lack of understanding of what Ueshiba was talking about, and the possibility that what students such as Shioda might have thought were quasi-religious ramblings by O-Sensei were actually his (tai chi classics-based) technical instructions. Could that be why Shioda said (something along the lines of) that he didn't really understand what Ueshiba was saying, until late in life?