Mark started the thread, and is assuming the IP/IS "worldview" as a premise:
- IP/IS is fundamental and necessary to truly effective budo.
- Certain historical "greats" had it.
- They didn't or couldn't successfully pass it on.
- Almost all current-day aikido is missing it.
- It is in the process of making a resurgence in certain circles.
I added the numbers. Let me address them first.
1. Not what I believe. You can have effective budo without IP/IS. As Ueshiba stated about religion, IP/IS makes it better. But, just because you have IP/IS doesn't mean you are necessarily great at budo. It all takes training.
3. Not what I believe. I think they could pass it on. I think that between Takeda making them keep it a secret and the Japanese manner in which they chose to pass it on contributed to it becoming very rare and almost extinct.
4. Yes. A majority. I'm certain that some people in aikido have parts and pieces to some degree or another, though.
Now, that out of the way, my point about this thread is this:
The aiki greats had to have devoted a great amount of time (solo, paired, etc) to training in some manner. Sagawa pretty much outright states it. I think this bordered on being driven. I know someone else who has been described as a training fiend.
Compare and contrast the top aiki greats with all others and you find that just because these aiki greats were driven, it didn't mean that they were necessarily bad people. There were others who broke more students than them. Sort of boils down to personalities in a different area than where being driven comes from.
For example, some top athletes are nice while other top athletes are cruel and obnoxious. Both sets are driven to becoming top athletes. Having this obs/comp/driven/whatever behavior to become powerful and budo strong doesn't equate to being a nice or not nice individual.
Separate from that is whether or not IP/aiki changed their personalities in the area of nice/not-nice, but that's another thread topic.