Hey Bpshiner, thanks for taking the time to respond to this. I absolutely respect what you do, and I freely admit that you know a lot more about the LSAT than I do.

I get what you mean about the underlying facts, and I think I understand why it's occurring, as well. Let's leave aside the extra stuff about the little details for now and return to the original point I had here: reading comprehension is by far the most important ability you can have, and it is what determines your ceiling for the LSAT.
The difference between our arguments is the scale of our arguments. Your argument is based on what you've experienced as an LSAT teacher for a number of years. Normally, this would give you a huge advantage in any sort of argument about the LSAT, but not in this case.
When you deal with a student, you are dealing with someone who is (I'm assuming) paying for the privilege of being instructed by you on the LSAT. They (or their parents) want them to be there and listen to you. Your argument would work perfectly if this were the target of this forum post.
It is not. The question is not "do you believe that your students have a ceiling", the question is "do you believe that
everyone has a ceiling on the LSAT?" This broadens the scale of the question quite a bit. It goes from dealing with only the very highest range (yes yes, the ceiling, I'll get back to that in a minute) to dealing with the entire range of scores, from 130 up to 180. It also broadens the target audience from merely those that put forth effort into studying to every person taking the exam. So, what does this in turn change?
It changes the meaning of "ceiling". Earlier, you said that my argument for reading comprehension seemed like a completely useless statement. When dealing with a set of people that want to improve, and put forth the effort, I agree with you. But when taken in this context, where ceiling has a different meaning, it becomes the only coherent argument. The only meaningful ceiling is one that affects the largest number of people, and would actually stop them from scoring a respectable score.
And the one ability that can actually create that ceiling is your reading comprehension. You cannot take this test well if you cannot read at a college level. Anything else can be learned with patience and time.