Even though you've done some nice work here, I'm reluctant to take those figures, particularly the change percentages, at face value.
There are colossal numbers of bots submitting posts and comments which metrics like this can't identify, which dilutes the real numbers. Of course bots would not be able to post to private subs, but it's less clear how much of the remaining traffic is human and how much is bots posting to empty subreddits as per the dead internet theory.