This current activity system was in place last Christmas. In addition, 1500 is more than enough activity to be a Hero Member. You must have gotten dates mixed up somewhere.
The dates are correct. I don't remember exactly how many posts I had but it was a lot cause many people were commenting on it.
I think the old system also had a time variable - where you had to be logged on for a certain number of hours and unlike now, it took a long time to accrue just 1 single day. So maybe I wasn't hero yet due to the time constraint which took a while to accumulate.
I don't remember exactly but I am certain I was Senior level and was very close to HERO cause I was looking forward to it and I am also certain I lost it all just cause I went on vacation.
And if you look at my post history from the beginning, I was not posting 2 word spam posts, I was simply very active. I posted long hours everyday just to have it taken away without any warning.
I should easily be a legendary member now yet I'm still not even a hero member.
The system put in place has always been like this and has not changed since it was implemented, in June last year. This can be confirmed with a search on the Wayback machine, or perhaps the below quote from Meni Rosenfeld:
time = number of two-week periods in which you've posted since your registration
activity = min(time * 14, posts)
I don't like it.
It embodies the assumption that any post above once per day (averaged over two weeks) is not contributing; which I do not agree with.
At the very least number of posts per day should be increased, e.g. min(time * 28, posts).
And you should consider more sophisticated metrics such as sum of f(x) over all two-week periods, f(x) being x / (1 + sqrt(x/14)) or x / (1 + x/28).
Time spent logged in will also be useful to include as a component.