My understanding of why this particular forum software is built the way it is, is to promote the ongoing conversation, and so editing the OP over and over instead of, for example, making new threads may be counter-intuitive to it’s design aims.
Also there is the option to make posts in to “Wiki’s” though this likely provides too much power for people to completely mess with the content.
It’s like something is required that is a middle ground of the two, for those that are using the forum to also provide important information that isn’t really announcement worthy, but interesting enough that you’d want to update things. If it were me looking at this, from a design perspective, I’d provide an “Update” option that essentially let you edit your post, but posted it as a new post and auto-archived, or at least default-hid the previous posts.
People could then browse back through what was said if they want, but the focus of the thread is moved to be from the context of the latest edit. It would help keep the conversation focused, but without creating a new thread every time you have an update, and without confusing people by altering the first post that could have changed a dozen times and, thus, made the 100s of posts after it now out of context.
That’s just my view, but the makers of Discourse may have plenty of valid reasons for choosing the things they have… doesn’t mean that they aren’t open to changing them!