Please excuse this interruption, but don't those four principles belong to the teaching of Shin shin toitsu do, i.e. the Tempukai?
I don't think they are usable to teach aiki like used in aikido or daito ryu?
And I don't think, Ueshiba osensei ever used them?
There are only 27 dojo of ki aikido all over Gemany and they follow a certain Yoshigasaki sensei. They don't claim to use "aiki", but try to just use "ki". Which is different.
So the way of using aiki / ki musubi and connecting using atari which I try to learn, simply doesn't exist in their aikido.
So I think those four principle are simply not designed to teach what for example Daito ryu calls aiki?
Just for perspective those four principles are A set to do with mind and body unification. You should look at this as the meditation side. Then there are other sets of principles, the next most known set being the five principles of Aikido. They work in unison. So, along with the other sets, plenty to learn.
When practiced as a discipline over however long it takes then it leads to understanding Aikido. That was Toheis aim. No different to others who formed their own teaching methods and principles to follow to achieve the same ends.
Doing so does indeed lead to discovering musubi, etc.
As with all styles and all arts there is of course the factor of good teaching and the factor of time. Most people in my view, especially in this day and age are looking for the 'quick fix' the 'easy way' and so we get hundreds if not thousands blaming either the teaching or coming out with excuses of 'i did that for x amount of time' and so I'm now an expert in how it doesn't work. To me basically they didn't keep at it and go through the necessary barriers. We even have experts based on hearsay and opinion but they can't do it, have never done it etc. Everyone in a hurry, wanting to be at the top, gleefully putting others down. A sign of the modern person rather than the state of the art.