I think this:
So we could assume that as time passed, Osensei still regarded transmission as important but gradually taught (with little change in effectiveness) a different part of the same subject more often. Clearly he observed the instructors he had created. Did he want them to just do kami-waza? Would he have approved if his instructors spent half the session talking about spirituality and kotodama before doing quick kagura mai demonstrations and claiming it came from the kami?
Could it simply be that Osensei gradually moved away from the hands-on teaching work and delegated it to the instructors he had created for that very purpose while he focused more on teaching the spiritual side for his retirement? If we are to believe Chiba Sensei, he watched them with the eyes of an eagle in the fifties and people have already described the founder flying into a rage when he saw his students not doing his aikido later on.
and what Chiba says later in the link you posted
I remember profoundly one demonstration he (Saito) performed along with other senior shihans in front of O-Sensei on the occasion of the New Year's celebration at Hombu Dojo.
He only did katadori ikkyo through yonkyo as plainly as he usually did in his class. He knew well the danger of doing something else in front of O-Sensei
Plus the different (not saying here better or worse) training methodology in Iwama hints to O Sensei had a clear image of a step by step training method, a house which had to be being built with both physical and religious materials. Bricks and concrete, from basement to the top.
IMO, what happened is his students, for various motives, built their houses with straw and sticks or, in the best cases, with bricks only. Faster, cheaper, easier, available to everyone.
So I would not say Ueshiba teaching/training ability was lacking or impaired. For me it was simply people didn't want to buy the "outdated" technology he was selling. Is not Ueshiba who changed a lot, it was his post war students who were different people from the pre war ones.