I have never trained with Yamaguchi Sensei, but I have trained with his son Yamaguchi Tetsuo Sensei, Yamashima Sensei, Endo Sensei, Tissier Sensei and Mimuro Sensei. All have different qualities and emphasise different aspects of Yamaguchi Sensei's style of Aikido. Common to all, is a strong centre to centre connection and emphasis on sensitivity and alive and powerful relaxation.
Uke and nage are two sides of the same coin and both are engaged in the same endeavour, moving with sensitivity and connection. This makes practice valuable for both. True, the denouement is the result of a set up and the resulting throw may appear contrived. On the other hand, resistance within the 'set up' is a form of disengagement and makes the outcome less predictable, perhaps even dangerous. It is not good training or practice.
There is a whole debate about goshin waza and Ki-no-nagare that has been going on - it seems - forever. The clip that Alex refers to illustrates the case and the confusion that for many is seldom resolved.
Aikido is a martial art, but it is not about fighting. In the thirty or so years that I have been associated with Aikido, I have seen endless examples on the mat of people trying to practice a mix of goshin waza and ki-no-nagare Aikido at the same time - and people wonder why they are not progressing! In the Ki Aikido, which is a large part of my background, this was jokingly referred to this as resisting with Ki - yes resistance is common to all styles.
In most of the films that I have seen of Saito Sensei, he starts a class with tai-no-henko and talks about distinguishing between goshin waza and ki-no-nagare. He does this to clarify that they are different forms of practice.
Hiroshi Ikeda Sensei often points out at his seminars that 'hard' and 'soft' are two ways of expressing unity, but it is the unity that is important not the outward form of expression. Where people are running around the mat trying to aikido each other, they are only struggling with themselves and each other. Of course I have done this, too; I know whereof I speak