This aspect of Tohei's aikido is fundamental to his particular 'way', others may have it in theirs but it is maybe not so apparent.
I spend a great deal of time with my students examining and practicing these principles, and you are right, they are not that easy to grasp - very easy to do when you have embodied the skill, but difficult to get rid of all the mind/body habits that get in the way of it happening effortlessly.
For me, leading ukes mind from the moment that they initiate the attack, is what makes the whole thing work. Lead the mind and the body will follow. The tennis ball effect is exactly as you describe, both powerful and slightly disorientating for uke.
I really enjoyed watching the video as I had not seen that one before. I wish I could understand Japanese, to hear his detailed instruction, I certainly recognised all of the principles being shown.
Yes, it was the first time I had seen that particular video and like you I thoroughly enjoyed it.
Isn't it funny as when you see one done from the way you understand you are looking at it almost in 3D and kind of say to yourself 'now that's what I'm talking about!'
Hence when I watch other styles I have to remind myself most of my understanding of what I'm seeing is assumption unless the person is communicating what they are doing.
This is also true the other way around when you see others commenting from a so called expert view when you can see by their comments they are well off the mark. All good learning both ways.
You know, before I came onto Aikiweb I never really used the term or thought of things in terms of internal and external as I used the terms hard and soft.
For me I thought you can't have internal without external and visa versa. We were taught to feel both and recognise both all the time and that both need to be in unison but no added significance. So it was all a matter and still is for me of what principles are being used.
When I teach a principle I teach how that same principle applies physically, how it applies mentally and how it applies spiritually. The effects of it inside and outside.
Anyway, gotta bounce, ha ha.