For the duplicate thread, I removed the extra one a while ago. However, I've just changed the name of the thread in question for the one still visible.
When it comes to the ranting you're talking about, yes, it's allowed, as long as the person posting doesn't break any of the Runescape rules or go against the forum Code of Conduct. In this case, I consciously decided to leave it up, despite the fact that it's a bit on the edge of what's acceptable, as the person clearly wants some help and needed to vent their frustrations at the same time.