Edit: So IF you had the 1000 merits, you might be Legendary at this point, but it wouldn't be guaranteed. I had to wait until about 1020 activity before I got that status, and that was before the merit system *whew*.
My account being a perfect example here. I had 1000 default merit and I think activity as same as the OP but I did not reach the legendary rank. Like you said it's random when one becomes a legendary while activity being in the scale of 950-1030.
@OP, you have a long way to go.Gaining 500 merits would take a few months unless you do something extraordinary.