As someone who has access to site metrics, I can confirm that daily user visits have been nearly halved since the days of G2 in its prime.
The site certainly peaked when Bionicle was around, and with it gone actively is at 50% of what it used to be.
With that said, aside from the dropoff after G2 activity has been relatively stable for the past two years. Some days are slower than others, and in fact the site is currently on a rise with more active users in the past few months then the second half of 2017.
So has it slowed down? Yes. Is it dying? Site analytics don't seem to think so.