I think your Devil's advocacy needs to be somewhat stronger.
The point I am making is much simpler than the point you are answering by citing Nishioka on rei (with which I agree).
Takeda taught Daito-ryu kata (or waza, if you like) and charged so much per waza. I do not think he was the kind of teacher who would expose himself to danger by reversing roles and taking ukemi from his own students. Ueshiba, also, did not do this, but for different reasons. Of course, Ueshiba also expected his students to become better, but he expected them to show this in the skill with which they attacked--and also the skill with which they dealt with the reversal of roles--to put it in your terms.