Greetings, all.
If I may, I'd like to share my experience with the TTCS over the roughly six years that I was a member in the Toronto area. I should say that I never had the opportunity to take instruction from Mr. Moy.
I've found that at the grass roots level, the members have been very warm, open and accepting. In particular, when my wife and I visited the San Francisco branch, we were welcomed, and as a guest, I was even invited to share my understanding of the moves. It was a great experience, and one of the advantages of belonging to such a large organization -- you can show up and take a class at any branch.
Regarding the content of the instruction, here's my take on it. The tradition from Mr. Moy is to teach a student what he or she needs to know at that moment, occasionally stepping outside the form, then stepping back into it when the old habit has been corrected. For example, I believe the squaring of the hips is designed to open up the joints of new students and begin the habit of turning. Once the joints have been opened that way, then the student can progress to opening up the kua, with less turning into the front hip, and more opening of the back hip (in front bow stance). As another example, the up-and-down motion is also temporary, to teach the student to relax into a sit at both ends of the posture (forward and back). The up-and-down is eventually reduced in favour of maintaining a root. This is my impression.
This is good, in that it addresses the student's specific issues at that specific time, and hopefully will lead to practice of the form with a more relaxed, open body, with more "internal" intentions, compared to someone merely mimicking an accomplished instructor.
However, there are downsides to this. 1) If a student is pushed into instructing too soon, he/she may believe that their personal, current level of instruction is "the form", and so that instruction becomes institutionalzed, especially if the student starts a new branch. 2) It can frustrate students when they are asked to change their previous form because the old one isn't needed any more. I believe this may lead the leadership at the TTCS to discourage the practice of stepping outside the form, and as a result, some instructions might become institutionalized as "the form". 3) Related to this, a number of students believe that the TVOntario book and movie represent "the form", but it is just a guide for beginners.
In short, I don't think that anyone should look at someone doing TTCS form and assume it's a good example of what Mr. Moy was capable of teaching. That student may be stepping outside the form at that point in time.
Regarding insularity, my advice to TTCS members would be: keep your eyes open, and read a lot about the basic principles of Tai Chi such as rooting, alignment, and so on ... from other sources.
My 2 cents. Thanks for reading ...
