Sometimes there are discussions where there's actually back-and-forth conversations between members (which unfortunately isn't the case most of the time), and if that back-and-forth is fast enough, it'd be easy to make 10 or more in an hour.
I agree with you that with back and forth conversations between two members it's actually possible to make more than 10 posts in an hour, but during those conversations we really don't care much about the constructiveness of the posts but focus mainly on continuing the conversation so that it can be helpful for both parties and also for the other members who later read that conversation.
I don't think rest has anything to do with posting. It's more a matter of finding threads that catch your interest and in which you can write something halfway decent
Rest has nothing to do with the posting in general but as humans we have limited energy and sometimes we really have to take rests in order get enough energy to think better. The interest in a thread is the most important thing without it we really can't write anything helpful at all. Sometimes we have interest in threads and we are also knowledgeable enough to write something in that thread but due to lack of energy we may not be able to make very helpful posts.