I'll personally go.. well the question is a bit unclear to me about where the true or false stands on.
Idea guys have no value if they can't bring their ideas to life or to have at least some kind shape, and the standard wouldn't even be a proper drawing or a narrative text, even the sketchiest of drafts could work, it'll have a shape that needs polishing, but it is a shape non the less.
Anyone can come up with an idea that another individual has imagined, but what matters is the execution and the way this idea is materialized or digitalized. So, ideas cannot be copyrighted, the product that comes out of it could.
But, if an idea guy is willing to shape their vision, have some kind of direction even if they won't be the writer or artist, for as long as they provide the resources and tools for that idea to take shape then they have some kind of value, but placing them in a paid position would depend on certain aspects such as how much are they actually providing.
Artists would likely hire a person who is both a writer and a idea guy instead of seeking two separate individuals, you know, kill two birds with one stone. Meanwhile, a writer "could" hire an idea guy, but since their work is already related to the creative process of generating concepts then I'll think is not a highly demanded position.
Idea guys, generally, make things according to what they want, since they have no artistic skill like drawing or writing, then of course they should be the ones paying since they are the ones with a vision, idea, concept and they are the ones wanting to give it shape... the ones with the interest is them, not the other two.
I believe the concept of "Idea guy" comes either attached to another field, producers, coordinators, researchers, marketing, investment, etc.
But returning again to the concept of IA kiddos and typing silly little prompts to generate an image with a bunch of database... no, they aren't needed. They are the truest concept of a lazy individual