> a complete inability to communicate the challenges and successes of a technology, technique, or theory to laymen is a huge demerit against a claim of expertise.

Hard disagree. A person can be an internationally recognized expert working on e.g. a novel mathematical theory useful for cryptography, without being able to explain any of it to anyone without a university-level math education.

I posit you're combining two orthogonal properties, expert knowledge and being a good communicator, into one axis because that's a useful combo, or the make-up of an expert that you'd like to know and/or hire.