There's some truth to the idea. At the same time, I've met plenty of experts who are competent and productive in their work, but incapable of concise communication.

If you sieve through their rambling, you'll notice that they do have a mental model. The problem is that the model is very foreign to other minds, and they do a poor job describing it.

This might be the reason that some people are more comfortable communicating with formulas than verbal descriptions. They are eloquent when they don't have to come up with their own words.