We have provision for 1 on 1 great debates. It is possible for the participants to decide themselves where the topic goes. It is also possible for others to be invited if the 2 agree. Otherwise others are not allowed to post.
I am curious as to why you think it is a difficulty to be focused as to topic. While every subject is interconnected it is clearly possible to focus on one thing at a time and, generally, that produces a clearer discussion.