I would have to disagree to some extent.
I have found that using the Aiki-taiso, developed by Koichi Tohei Sensei, are an excellent way for one person to practice for aikido.
If you focus and try to understand the movements (not just do them for the sake of doing them)and their applications to technique, they help you connect your center to your arms legs whatever comes in contact with uke making you much more powerful. It seems to have made me more subtle.
I just wish that when I started Aikido that I would have been exposed to these exercises, I really think it would have helped me with coordinating my mind and body.