Well, you used the phrase "learning tool", which is fine as far as your description goes, I just question how much they really contribute to learning.
The number of real masters of this stuff is very small, relative to the available pool of practitioners, which wouldn't be the case if all the people who have been exposed to ki tests made good progress. The existence of various tests doesn't seem to be much of a factor in getting people to an impressive level of skill. Some of these guys, like Chen Xiao Wang in particular, are frighteningly powerful. You don't get that just from being told "keep weight underside", and then a few years of pirouettes and you're there. There are bigs chunks of fundamental information missing from the basic stage to the impressive power and ability stage. That all-important information is very closely guarded.
No, I agree that you don't, but I attribute that more to the student/teacher relationship than the methodology itself. For the record, I've seen plenty of people who have learned things using the Tohei method that appear (key word) at least as powerful as Wang does in the film I've seen of him. Hell I
can even do a lot of the 'trick's he demonstrates. Like you said, just being told to 'keep one point' doesn't help if you don't already know how, but in a class these things are explained and actively taught.
Seems to me that you may have made up your mind about this stuff before experiencing it properly, I could be wrong but that's how it's looking to me at present.
Put it another way. In Tai Chi, the chi kung exercises are ki tests as are the forms themselves. My Tai Chi teacher used to ask us to stop at any point in the form and he would point out weaknesses in what we were doing, he also had us practice 'ward off' against punch bags to 'develop our chi' though he never said how exactly we were to develop it, just that hitting things would do it. When I went to aikido I found someone who was actually explaining all these things in a way I could understand. Imagine a Tai Chi form of X moves and your teaher happened to notice that all his students found it helpful for developing their overall internal skill if he singled out one or two movements of the form and had them work on those in a more focused way. Later when they have absorbed this info he notices that other movements seem to help when they are focused on. Eventually he gets to a point where he no longer has to focus on specific movements which seem the most helpful in teaching the internal skills because they have learned them and they can apply them however they choose. The Tai Chi teacher is developing ki tests (or in this case chi tests). All that has happened in the ki soc is that the ones developed by Tohei Sensei have become a standardized part of the curriculum.