I would say yin and yang come from one point. They are one, inside and outside.
Anything in me exists before between me and thee so obviously that would apply to Aiki or anything else so I fail to see any other significance to the statement if there is any.
Don't know what the significance of bouncing off is apart from a skill based on stillness. Hardly all embracing Ai ki as I see it. Part of maybe but wholly? No, not to me.
Valuable? Yes. Limited as far as Aikido potential? Depends solely on your intention and purpose.
This would help with all the above conjecture and missing information: