I would strongly suggest doing research about Ueshiba.
For instance, Mochizuki started training with Ueshiba around April 1931. Mochizuki was awarded the second highest rank/scroll from Ueshiba in June 1932.
Tomiki started training with Ueshiba around 1926-1927. He trained off and on until around 1934, when he moved to Tokyo. He trained until 1936 when he moved to Manchuria. Tomiki received 8th dan from Ueshiba in 1940. Start to 8th dan in 14 years. (And that's not even getting into the actual training time Tomiki spent with Ueshiba in those 14 years.)
There are other instances of Ueshiba just handing out rank when you dig into the research.
In the old days, Ueshiba did not accept anyone without any martial art background as students. If you look at the backgrounds of Mochizuki, Tomiki, Shioda, Shirata, Tohei, Akazawa, you will find that these gentlemen are/were competent martial artists even before joining Ueshiba. I believe the ranks handed out to them were based on their skill set rather than the time they put into training with him. There may be some exceptions which I am not aware of. Basically, we are looking at different set of standards - then & now.