Just an observation, but when @luceos, for example, made this post, I got two notifications (both with email and in-app badge indicators) — replied and posted — for his single action. That had me a little confused at first because of the redundancy. I kept looking for two different events.
I'm not sure how you would configure it, but it seems to me Flarum should be able to tell if a 'reply' and 'post' is done as a single event so only one notification is given in that case. I think "replied" would be the expected result.