Have been wanting to ask why is it that most users here their activity is different from their post count. For example you will see some user having the post count of 500 with activity of 125 why is it like that and what Is the course?
You can make 100 posts a week but still you won't get more than 14 activity points within 2 week even if you can make 200 posts within 2 weeks. Activity is somehow increases when you make around 14 posts within 2 weeks and that's an hard limit.
It won't increase more than that within 2 weeks, just keep in mind that you will get 14 activity points per 2 weeks and 28 per 4 weeks. Activity is needed to rank up on this forum and it's somehow dependent on someone's presence and active post making but it has some limits.
The ones who make 500 posts won't get 500 activity points because of the 2 week 14 activity limit. That's why the example you mentioned in your post had 500 posts while only 125 activity points. Activity points are needed to rank up but if someone earns 4000 activity points and no merits then still that user can't rank up.