DH

Ueshiba was training with Takeda into the 30's
The total days of training in seminars have been counted to add up to 70+ to 90+ days depending on who's counting.
It doesn't count all the private training. More important than those days are the days he kept training with his own people. All of those early guys only saw Takeda now and then. They kept training over and over practicing. That's probably the main source of their improvement.

As for 1922 period. I disagree with some people's assessment.
I do not believe that Ueshiba had aiki until then. And it is why after Takeda's long stay in Ayabe that Deguchi was so impressed by the aiki of Takeda's Daito ryu that he suggested Takeda change the name to Aiki-jujutsu. Why? because he stated the aiki was what was so magnificent. Takeda did change the name.

Some want to suggest that it was in Ayabe that Ueshiba was given jujutsu. Personally I think Deguchi and sooo many there knew and had seen all too much jujutsu, and that they were not impressed by more waza. I believe Ueshiba learned jujutsu with Takeda until his stay at Ayabe. During that long live-in period Takeda gave aiki to Ueshiba and only after that...did he allow Ueshiba to teach.

To follow that logic to Stevens quote- I can only say that making an argument that Daito ryu jujutsu would make anyone invincible- I find completely ridiculous.

Daito ryu aiki is the power of Daito ryu and the power of Takeda and thence Ueshiba's invincibility and Deguchi's amazement at Takeda's what???
Aiki.
Apparently, Deguchi got that much....loud and clear, if no one else has since.