Yes, you are perfectly right that if one has a « vision » regarding what a thread should be and how on-topic to stay, it implies active moderation or as I usually say, « gardening ». We are very good at that in our Facebook group and it’s something I’m comfortable with and actually enjoy. In our community it’s rare that somebody out of the blue blows up about this kind of thing unless there are other major difficulties involved.
Thanks for your take regarding the fact that there don’t seem to be ideal « norms » about things like thread length!