The principle of Aiki which means absolute non-resistance, manifested in timing, body positioning, leading, blending, Etc.
Your other points have been ably answered already, so I thought I'd pick up on this one.
the principle of aiki? That, for me is the heart of the question, and that's what I've spent >20 years trying to understand. I suggest to you that it is a legitimate inquiry--that reasonable people can have different views, and it's not an insult to anyone's teacher to explore different ideas.
Your definition of aiki is widely shared and up to 10 years ago I would have agreed with it. Timing, body positioning, blending: over-simplifying a bit, all adding up to getting out of the way--and then using uke's over-committed attack to lead them in a direction they are already weak.
Which is all very well, but what if uke doesn't over-commit? What if uke has actual training and delivers a fast follow-up attack?
When I joined Gleason Sensei's dojo I found that he and just about all the other ASU teachers I met had a very different idea of aiki. The aikido I've found in the ASU focused much more on immediate connection and immediate kuzushi, and I was taught to look for those principles in every technique. So even in a movement like tsuki irimi-nage, where the initial irimi movement doesn't require touching uke at all, as soon as the touch happens there should be connection and uke should be off-balanced.
Frankly, the things you keep emphasizing in your posts don't seem to me to reflect the aikido I've found in the ASU. Yeah, body positioning matters--because it puts you in a place where you can connect and take kuzushi. Same with timing and blending. But what knocked my socks off 10 years ago wasn't the elements you list but how they're used to create connection.
These days, most of the people I work with are involved in the IP/IS work, and that introduces a new idea of aiki--that you create aiki in yourself and then use that to control uke. I've found these ideas to be continuous with the approach that already existed in the ASU and that teachers like Ikeda are still pursuing. The IP/IS idea of aiki adds stability and centeredness before the attack and provides a vocabulary and set of concepts for what it means to "take center", "connect", or "take balance"--concepts which are embodied as physical skills and which can be trained with specific exercises.
Note that Endo Sensei seems to be talking along these same lines in the video linked to in the "stance of heaven and earth" thread. I talks about not bracing yourself or being "on your guard", but standing centered in a stance that "connects heaven and earth."
You've picked up the idea that IP/IS stuff is static, but that's nonsense--the whole point is to move dynamically while maintaining your center and controlling uke's. There is practice that starts from a static position, but that's practice--no more "realistic" than kokyu-ho.
Finally, on the subject of the big cooperative throws, which seems to be a hot button with you-- People I respect highly don't believe in them, but I'm not there yet. I see a lot of value in them, especially as a training tool early on. You've seen it: people arrive at the dojo falling over their own feet, moving like stick men--and within 6 months their whole movement and posture is transformed. A lot of that is from ukemi. The flexible tension you need to deal with the mat is the same as you need to have connection with your partner.
Large, fast attacks are useful for learning timing and body positioning (which are
important--just not the whole story). What's more, they're wonderful for learning to apply the IS/IP principles under pressure. But they're also a training tool, and they're only going to take you so far. You should expect that as you get better and as the attacks get more realistic, nage's movements are going to become smaller and more direct. If you remain wedded to big movement for the sake of big movement you'll always be limited, and you'll never be able to deal with a real, skilled attack.