The quote mentioning "straining hands" is as follows:
Fumiaki Shishida wrote:
Based on examination of these 37 passages, this expression refers to the usage of the hand blade(s) in order to break balance, and it is the same as the skill of aiki, which is, in Daito-ryu, the skill of breaking an opponent's balance in a flash by straining hand(s).
"Hand blade" obviously refers to "shuto" or "tegatana". I suspect Shishida is referring to hand positions here, and probably the English he was looking for was "splayed hands", i.e., the "asagao" hand formation. It would be referred in idiomatic Japanese as "te (yubi) wo haru", with the verb "haru" which can mean both "splayed", "spread", as well as "strained".
Of course, Dan Harden's point would remain that merely splaying one's hands would not "break the opponent's balance in a flash". But, by the same token, would we expect any reasonably experienced aikido person to define "kokyu wo ire" as simply "[using] the hand blades to break balance"? Much less an 8th dan Shihan of Shodokan? Perhaps Shishida is being somewhat vague/literal here in order to dumb down the article for his audience.
Regarding the nature of the whole study, I have one concern that could be addressed by providing the original Japanese of the notes. Shishida here (and the following discussion) attributes all the commentary in the notes to Ueshiba himself. I feel that might be a shaky assumption. The notes are clearly Takeshita's notes to himself, to help him learn. As such, they're not likely to be overly specific, particular in the pithy idiom of pre-war written Japanese. Does it actually say, "These are techniques that Ueshiba said could be used against judo"? Or, is perhaps that simply Takeshita's own interpretation of what he was being taught. We know that Ueshiba's teaching style, particularly at this early stage, was not very full of explanation and exposition. He'd show a technique, maybe twice, and then onto the next one. Perhaps Takeshita, conversant with judo, recognized whenever Ueshiba used a particular judo set-up to demonstrate technique/aiki/kokyu, and thus cataloged this particular techniques together. Creating his own "syllabus", as it were, just as every other student of Ueshiba was doing. In other words, is "counters against judo" Ueshiba's words, or merely Takeshita's take? And so further, just how much did Takeshita himself understand about aiki, and how is that understanding (or lack thereof) reflected in the notes he left?