George S. Ledyard
I can pretty much guarantee that someone training two days a week at the dojo and doing all sorts of solo training at home, will only be marginally, if at all better at his paired practice than the person who just trains twice a week and watches TV at home.
For someone familiar with the amount of solo training that developing internal skills requires, I am really surprised by this statement.
Developing an aiki body aside, I firmly believe that time spent on general cardio training, practicing solo footwork/movements, visualization, and even studying books or videos can have a measurable impact on one's aikido.
Is it a substitue for paired pratice, especially under the supervision of an instructor? Clearly not. But it has to be far and away better than spending the equivalent time watching TV.