This is different from what you imagined I said in two key respects:
1) "by and large" does not equal "are always"
It's close enough that the meaning is essentialy the same.
2) I did not say that the best dancers are the best teacher.
I never said that you did (now who is "reading things that have not been said"?). I simply used this proposition to demonstrate your lack of logic.
I compared those desirable as JUDGES to those desirable as COACHES. Both skills can well leverage personal dance ability, but both require externalizing it to a situation that one is not physically a part of - which is one of the major areas where good dancers may fail in judging or coaching.
Desirable according to whom and on what basis? Desirable because of their familiarity with your "dancing" thanks to those sesssions for which you paid inflated fees?
You cannot externalize ability; you can only externalize experience. You have put yourself into a position where you must argue that teaching experience makes one a better judge than dancing experience alone.
I'll give you an example from a comp that I attended earlier this year. I was with a different partner then, a very young woman with only a year's experience, almost none of it in Latin.
As we watched the Latin competitions, this supposedly unknowledgeable dancer correctly identified the winning couple in four of the five heats that we observed (I only picked two) and these were closely matched competitions.

jj