Personally, I think it’s the “topic” (noun) that is the issue, not the “post topic” (verb). We have a new community that is not yet used to Discourse’s (yes, very opinionated) vocabulary and I have heard more than once that they are a bit afraid to start a new “topic” because it seems like it might be creating a new category – or changing the structure of the site in some way that they don’t intend. While I understand the logic in differentiating between a topic and a reply, for us, it’s not as important as removing every possible obstacle to participation.
I’m glad to know that it’s possible to change the text and think I will probably change it to “thread”–which is something that they recognize from email and feel they have personal agency over.