My recommendation is to investigate the internal skills, with an instructor who is willing to present a thorough grounding in the basics, in the context of the art in which you're primarily training. You may decide you already do all this stuff, or are at least doing enough to be satisfied, or you may have opened to you a far wider range of possibilities for your practice than you ever imagined.
At the moment, there is no complete expert available to westerners
who "knows all the stuff" and who is teaching how to do things. The amount of knowledge and the method of presentation vary, but you put your finger on it with the idea of "basics". No matter how good some instructor thinks they are (and maybe some of them have up into "moderate" range on some areas), my opinion is that aside from "basics", that's about all anyone can expect to get at present. The skills are ancient, but this generation of instructors is a very small pool and the upper level of skills is limited. Yeah, I'm an iconoclast.
So that being said, I'd agree with all that you said and I'd caution about anyone assuming that they "already do this stuff", even to a small degree. Over the many years of many time-wasting mistakes, I've learned that the safest approach to training is to constantly have the thought in mind, "What am I doing wrong?". Anyone who dismisses that analysis with a "well, I've already got part of it, so I don't need to concentrate so hard" is suicidal, IMO.
Anyone can learn weak approximations of the static or near-static starts of ki/kokyu usage in reasonably short order. Learning to actually do all these things while moving, and I mean true movement from the center, takes a lot of time and effort. The actual full-blown ability to do even the static level of the demonstration ki/kokyu takes longer than it first appears because the training of the body causes changes that a beginner has no concept of, at first.
I.e., I'm not trying to throw water on anyone, but I'm really trying to save people some wasted time and effort by pointing out (maybe too many times) that it's harder than it looks to get it right.
I will say that I was extremely encouraged, if not outright impressed, but the level of ability and focus I saw by some of the Aikidoists at the workshop. Whoever your student was who assisted me in the preliminary discussion on "unbendable" arm... he was bulletproof throughout the demo. I was impressed. At that rate of acquisition, I expect great things.... but I'll never compliment him needlessly because the last thing I want to do is potentially slow down his efforts by telling him "that was perfect!".
Because there's further that he can go.