I am moving this to Feature because what you are describing is a feature request, which likely could be addressed with a theme component. I don’t think it’s likely to become a core feature given that Discourse is built on the premise of facilitating long form communication, in paragraphs.
I don’t disagree that sometimes it feels duplicative and a bit frustrating to have to write both a topic title and post content when starting a topic. But on the other hand in almost all cases it will be worthwhile for others wanting to help or respond to have at least a few sentences to respond to.