I am both a technical writer and marketing writer (I am a PhD with a background heavy in CS, Mathematics, statistics and mechanical engineering, with 40 years experience).
I have written manuals, spec sheets for products, instructional materials and advertisements for products and services, including brochures and globally published ads that have been successful.
To me, marketing is not fluff, or rah-rah, or jargon-filled. I can avoid all of that and still sell product. In my view, the point of marketing is to convince a potential customer with a specific problem that you and/or your product or service can solve their problem, without lying to them or trying to con them into buying something they do not need.
I will agree with your front of the house colleagues, and I will note a common maxim in sales I learned 40 years ago is 100% true: Nothing happens until there is a sale. We can develop the best widget ever made, but if we don't sell any, we've got nothing to do, and widgets don't sell themselves, somehow and in some way potential customers with a real pain that can be relieved by our widget must find out we have it, and what it does, and how it relieves their pain, or they won't buy it.
Any channel by which they can find that out is a valid channel to be addressed by marketing, including your technical documents if they might find them by a search.
The case to be made requires you to distinguish between "rah rah" writing, and legitimately pointing out the bigger picture about the product and how it helps people with a specific problem.
So (making this up) maybe your A/D sampling chip can oversample at 100KHz and this lets the hardware synthesize a more accurate 44.1K samples per second. That would be a "fact", but marketing may want to emphasize the consequence of that fact: A cleaner audio signal with fewer aliasing artifacts or harmonics, suitable for higher quality digital music, sound effects and soundtracks.
That is a problem people many people might want solved, and searching for spec sheets, this tells them yours is the A/D sampler they want. Finding out this is used by your X, Y, Z clients may send business their way and ultimately increase your orders.
I personally don't like anything I would characterize as untrue or empty rhetoric or misleading, but I don't mind covering every opening that might reach a customer with a layman's explanation of what our products do and how they help.
I am not defending marketing by saying "we are in business to make money," I sincerely do not believe that. It is a far more difficult proposition in my view, we are in business to satisfy customers at a profit, without exploiting them, our employees or society at large. And that is so difficult, every avenue of recruiting customers, without lying to them, is worth exploring.