Again I disagree and at the risk of beating a dead horse - when and by whom did this change occur. Both Takeda and Ueshiba M. taught in very traditional ways for jujutsu which meant that deshi spent a lot of time receiving technique.
I'm curious to learn how two known "innovators" taught in a "traditional" manner?
FWIW, It's reasonably common knowledge in koryu circles, where old teaching methods are usually preserved as much as possible, that the uke role in both armed and unarmed training is most often filled by the senior who can then control the outcome and provide the highest levels of instruction.
I'd suggest that this change began with innovation in judo and continued through the intervention of government. Dig through the research in historical Japan and observe that more modern forms of budo practice involved a much higher student to teacher ratio, which makes it very difficult to continue such a practice. When you add to that the use of judo and other forms of "traditional" instruction in schools to inculcate "Yamato-damashii" where formality and obedience was was the real learning and order of the day, I guess you could say it's not all that unclear how this changed.