A report happens when one person presses it. It registers as something that requires action, which we'd then have to ignore until enough people also report the same post. An 'off topic' button wouldn't start a report until enough people had pressed it, and could also be public so users could see when others were thinking a thread was being dragged OT. Colour code it to bring people's attention to the need to self-moderate. Only make it available to those who have been here several years so it's the long-term population who get to help shape the discussion structure.
View attachment 2014
In every day use, readers would start to yellows creeping into the thread and know that users are wanting to be tighter with topic. They might change at that point, start their own new thread to continue the discussion (we wish!), or carry on, at which point more people would start to feel the thread was going OT. They'd vote, a threshold would be reached, the button shows red to show it's OT (please stop replying until we've had a chance to spawn a new thread) and a mod report is filed saying a cleanup is required. Importantly users will have a visual clue to not reply to OT posts which otherwise is difficult to notice - requires a reading of the title and its subjective interpretation.