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
Do you know if the default values of ranking up were 500, 250 etc? I've hosted SMF forums before, but nothing compared to this forum, obviously. I've only ever done it for testing purposes, and setting them up for others. I can't remember the default values as it was a number of years ago now.
Yeah, I think that was the concern at the time many users were spamming their post counts up, getting to a "respectable" rank, and then attempting to scam, and I believe a few new users to the forum were falling for it. I'm sure there was a number of reasons for it to be implemented, and the discussion that the OP linked shows users discussing that.