as far as power and Ueshiba Morihei, seemed he got plenty, but of the million strong aikidoka past and present, not one exceed him in ability, at least i have not heard of one. it's kinda sad don't you think? just think, if every generation of aikidoka where the students are less in skill than the teachers, what will be a few generations from now? it's all math and all down hill.
Don't you think that the superiority of o'sensei to all subsequent aikidoka can be attributed to the unique life he led, in a world which no longer exists? I.e., he was a man of means - hence he did not have to work, and so could freely devote his time to budo; he was in the army - in a conflict in which more modern means of killing were not at the fore; he lived in a society in which the martial arts were studied/practiced very seriously by others, and conflicts/challenges took place fairly regularly (granted they do nowadays, but not really among aikidoka - they are deliberately avoided, where possible).
I don't think there is anything at all in the argument that aikidoka will decline in ability as time progresses: ability is a result of natural talent, and hard work, and I am certain that there are people who have far surpassed their teachers in understanding of aikido.