My impression is that modern aikido is built on top of many work arounds. Don't know why but such know-hows help techniques work easier and better. Please see this. At the end of the video, the teacher says
1. just turning this.... (this helps.. but what about not turning at all?)
2. only use the weight of arm.... (what if add body weight?)
3. put it on top of him.... (only weight of arm? or ??)
It's not so hard to put nage's weight on top of uke through arms. You can instantly feel like uke is standing on the air regardless of how hard he grabs nage. Untrained uke can't resist it. But if the uke do some solo exercises, it's damn hard to do.