I was referring to much of the PSIA materials I've read through (and some CSIA). Lots of high level concepts without a lot of specifics on how to move your body parts to achieve the goals.
Changing the amount of flexing and/or the angles of our joints isn't really going to get the job done when it comes to really managing your fore/aft at will. Also, there are direct contradictions to some of your examples. For instance I can be "low" with most of my joints quite "closed" and be forward or be aft; depending on the positioning of the joints in the stack and/or what part of the turn lifecycle I'm in. I know what you're getting at, but once again, referring to joints as opened or closed is only speaking to the "positions", not the movements. How we go about opening and closing those joints should not be assumed. There are right ways and not so good ways...
And I'm not challenging you (or anyone else) just to be snarky, but rather to continue the conversation that there are many "nuances" to how to actually accomplish much of what is taken for granted in a lot of these discussions. And to point out how often these technical discussions aren't actually referring to true body movements.
I'd like to play...
I can't speak to the PSIA or CSIA materials because I have not read them. I have, however, experienced a lot of ski instruction over the past 2-3 decades. And I assume that most, if not all, of that instruction was PSIA based. I will agree that there are many instructors out there who have told me a certain thing without telling me how to accomplish this thing. Or why. There also have been a good number of instructors that have given me coaching tips/pointers that has improved my ability to ski more efficiently (and subjectively better in that I can ski faster and in more difficult terrain for longer than I was able to do 15-20 years ago). While I have had some excellent coaching over the past 15 years, I have not had the opportunity to get coached over the course of an entire season (or more...) - I am sure that this type of coaching would allow me to dig deeper into movement patterns and such.
Some of the instruction that I have heard about (or witnessed) over the years probably is just the type of thing that pushes your buttons:
"Balance against your outside ski" YES, I want to, but what does this really mean, and how do I do it?
"Get inside your skis" Wait, what? How?
"Steer your skis" I have never really understood what this means
"Use the entire ski" I thought that I was using the entire ski
"Angulation/Inclination/Counter" - I never could grasp the difference between these. I mean, I know that they are different because everybody tells me that sometimes I should do one of them and sometimes I should never do it.
"Dive into danger" Why would I want to do that? (Interlude for a crude joke:
Why do women develop wrinkles at the corners of their eyes at a younger age than men. From saying to their boyfriends: "you want me to do what?" Never mind...)
In none of the above examples is there any instruction/direction in how to achieve the stated goal(s).
Then there is the dabbling that I have done (without full commitment, to be fair) with learning systems that have you learn very specific movement patterns such as you are (I think) referring to. I have picked up some great pointers from these systems, but ultimately felt turned off by the often dogmatic approach (e.g., the teaching systems that imply that if you are not doing specific movements as described, then you cannot possibly learn how to ski).
Here is where Tom Gellie comes in (for me, at least). I had never heard of him and was skeptical when I first started reading this thread. But I figured that I had the time and a few dollars to spend and so I subscribed for this month to watch the videos. It is definitely a commitment to watch through them all (and I am only halfway through...). There is a lot of material, and there is a fair amount of overlap. My guess is that eventually Tom will organize these videos in a fashion that allows for more coherent watching. But here is the thing for me: for the first time, I am getting an understanding of the why/what/how of what I am doing on skis. Maybe it is the way my mind works (or where I am at in my path of learning to ski) , but I fell that he is giving details on movement patterns. And his explanations make sense in terms of the physical forces that are working for and against me when I ski. I have been able to get on the snow only for a few runs since I started watching, but I can tell that there is plenty for me to play with to improve my skiing. More importantly for me, I am gaining understanding in what is really happening when things go wrong. So I expect to get more than a few "Aha" moments as I play on the snow. So for me, it is his approach and method of explanation that makes it worthwhile.
Is he telling me to do anything that is radically different? Nah, I don't really think so. I pretty much think that there isn't anything really new or revolutionary in ski instruction. And there hasn't been for a long time. And, in my humble and possibly ignorant opinion, all the different teaching systems end up with the same end result.
I'll apologize in advance if anyone thinks that I have been snarky or condescending. I just felt the urge to put these thoughts down.