If I'm remembering correctly, and I'm pretty sure I am the ranking system previously to this was merely just based on post count. I haven't hosted any Simple Machine Forums for quite some time, but it might well be the default ranking system used.
I can confirm that the default SMF ranking based on post counts. I have tested SMF several times and found out it's too easy to rank up (if anyone wants). Introducing activity counts was a good move.
Two years ago, I was hanging up in another forum for few weeks and that was hosted using SMF and believe me or not, I have seen people to post crazy amount of posts. In a week some people made over 1k posts. So, according to our activity requirements they are Legendary in a week LOL
Anyway, the evaluation of our ranking system is better in my opinion. Especially the last edition of merit requirement. At the beginning some users were totally against it but now it seems, "The hell has frozen" :-P