There’s a video where Mr. Zimmer did a round table with a couple of couches worth of other film and TV composers. They all groaned about film producers saying “Just let me hear the idea, just a piano is fine, I’m very creative and experienced; I can imagine where you’re going.” And if the composer falls for that, the composer will inevitably hear “I dunno, I don’t really get it, it just sounds like a solo piano.”
I don’t think decent mockups are optional for that kind of writing.