To a certain extent all scientists communicate their work to other people, even if it's just to their funding agencies, colleagues, family and friends. However well - or badly - they do it is not the point, it still counts as the communication of scientific ideas.
On the other hand we have the professional science communicator, who still needs to be a trained scientist to degree level, but who has carved out a career by translating complicated concepts into palatable (but not "dumbed down") ideas.
I wonder if it is confusing to members of the public to see science communicated by people who talk about the work of "scientists", but don't profess to be one themselves. [I use the term "public" with that kind of cringe that is reserved for times when I'd like to find a better word to describe "lay-people" but can't think of one.]
Particularly for the case of school children, doesn't this just create an extra barrier between themselves and the "real" scientists? It's all very well that the communicators are generally young, gender-balanced (as a group, that is) and enthusiastic people, but do the audience walk away wondering what the "real" scientists are like? Do they still assume that they are white middle-aged men like they see in textbooks and in pictures on the classroom wall? (Newton, Einstein, Rutherford anyone?)
It's great that we now have "real" scientists who are also fantastic communicators on TV, and I think this is definitely the way it should be. But... does this make 'science communicators' redundant (except perhaps in science journalism)? How much does credibility matter? Should science museum presenters be part-time researchers? What if they are presenting something out of their 'field'? What if a scientist is presenting something that isn't their research?
I would love to believe that we simply play complimentary roles where communication experts can help science experts and vice versa. But of course, when it comes down to it the communicator has to make money from this whereas the scientist doesn't. That, if nothing else, must surely change the game.