I think that perhaps the very best comparison that can be made is this:
Hundreds of people who have rowed boats in this manner (as the recent videos have shown) and have equaled Morihei Ueshiba's skills and abilities vs Sokaku Takeda teaching Daito ryu aiki specifically to certain students.
Then, perhaps compare the hundreds, or more, of spiritual people who have done torifune and equaled Morihei Ueshiba's skills and abilities vs Sokaku Takeda teaching Daito ryu aiki specifically to certain students.
Reference Morihei Ueshiba stating that aiki "completes" religions. Note that it isn't the other way around.
Reference Morihei Ueshiba stating that he was a man of budo and not a religious man.
So, then when you find 0 people in the former categories and 6-10 people from Takeda's category, perhaps a closer look at aiki as an internal method to remake the body is warranted? Perhaps it really isn't the actual act of torifune that gave Ueshiba his skills and abilities, but rather that Ueshiba's aiki exercises "completed" torifune ... torifune was the vehicle for which Ueshiba used to practice and get better at aiki skills. Just as he did with farming. With chanting. With swinging a jo around.
Course, if someone wanted to spend 40 years rowing a boat to get aiki, that's their choice. Almost like spending 40 years doing torifune ... or 40 years doing techniques ... What was it Einstein said about insanity?
Of course I can't speak for anyone else, but this seems a little obvious. I don't think it's a matter of whether or not rowing a boat gives people IS (I haven't seen that said yet, at any rate), it's a question of how might one begin to approach IS through this rowing exercise. The best way is to practice with people who have IS and apply that learning to the exercise. Given that understanding, what might the exercise lend itself to? How do people approach the exercie?
I rather like Greg's remarks about pushing with the "yang" part of he body instead of the "yin." I think I can see what he's describing.