As I understand it, the method is basically that of apprenticeship, which demands one on one interaction to glean mastery.
That's exactly my point. How well does this method work? Of the people who studied the closest with the founder -- living in the dojo, training several hours a day, getting more hands-on time with him than anyone else -- how many of them could do what he did? The general consensus is that some
of them picked up some
ability to do some
of what he could do. If so many of them couldn't get it with that kind of access (and we are talking about people who were in many cases already highly accomplished budoka in other arts), then what chance does the guy training 3 days a week with a student of a student of a student of the founder have? Virtually none. Sure, he is doing the movements that look somewhat like the outer form of what Morihei Ueshiba was doing, but there is no substance there. It is almost as if they are doing two different arts.
Contrast that with an art like BJJ, just to take an easy example. The guy training a few times a week with a typical black-belt will, in a few years, have some usable skills. He will be doing in essence the same art that Royce Gracie is doing; he just won't be doing it quite as well. But he will know that there is an end goal and it will be clear that he is making progress towards it, despite the fact that he might never have trained with someone even close to Royce's level. He doesn't need to, because the pedagogy of the art is good enough that it can be passed on without direct one-on-one training with a master-level practitioner. Of course, to get to the highest level you need to train with the right people, but I'm talking about the average guy training in the average dojo for just a few years.
What can a guy training three years in the average aikido dojo do? He can perform a number of choreographed techniques on command with a cooperative partner, and can probably take the falls for those techniques as well. That's about it. Unless he already knew how to fight coming in, odds are that he still can't fight very well, and more importantly, he has no understanding of how to apply aiki in any kind of spontaneous situation. He is just doing empty forms, but he thinks he is "making progress" because the only way progress is defined in his art is through ranking, and the only requirement for ranking (other than loyalty to the group, which is actually the primary requirement anyway) is to look good performing forms on command with a cooperative partner. Not only is he not making much, if any, real progress in the direction of what the founder of his art was doing, but he probably doesn't even have any idea of what that is.
If you look around for the people in aikido who are the exceptions to this, how many of them do you see getting other training to fill in the very large gaps in aikido's pedagogy? And who are they going to? People outside of aikido who have developed a pedagogy for teaching the things that aikido should have taught them but didn't. Even Koichi Tohei, by all accounts one of Ueshiba's most talented students (and by some accounts the
most talented one) had to go elsewhere to learn what Ueshiba didn't teach him. After doing so, he started teaching what he learned there as part of aikido, much to the chagrin of some. What does that tell you about his opinion of aikido's default pedagogy?
If you keep training in a system that has been proven mainly to create people who look really good performing complex techniques on a cooperative partner, that is the result you should expect from your training. If you want a different result, you need to train differently. It's that simple.