I think most agents and editors wouldn't be impressed by an author trying to tell them about the market for your novel, or that there's no competition, or whatever. They probably know far more than we can (apart from anything else, they can afford Nielsen BookScan) and seeming to teach your grandmother to suck eggs is not a good start to what you hope will be a relationship!
Whereas if you're writing non-fiction you know a whole heap of stuff as Maria did, that they can't, about who might buy your book. Also your own expertise is relevant, in that it gives you what the US calls 'platform': you can promote your expertise, as well as the book.
So with fiction, I think I'd restrict my pitch to explaining my novel as zingily as possible, and add in anything about you that would catch a publicist's attention: those are the two things an agent would be interested in.
Emma