There are not that many people in the situation indicated in the OP (enough merits but not enough activity to rank-up). I make it (as of last Friday):

-   8 Heroes, lacking at least the minimum current value of the range necessary to become Legendary.
-   19 Sr. Members lacking activity for Hero.
-   15 Full Members lacking activity for Sr. Member.
-   23 Members lacking activity for Full  Member.

-   460 Jr. Members lacking activity for Member. (*)
-   3618 Newbies lacking activity for Jr. Member (*)
-   185 Brand new lacking activity for Jr. Member (*)

The core currently "affected" is only of around 65 profiles (Member rank onwards), which is not significant enough to suggest a need for a change in the activity parameter in relation to the merit parameter.

(*) The lower ranks have a larger base, but activity is trivial to reach for them in a short period of time. Numbers are larger here, but many of these account (not all) correspond to demoted accounts by means of deleting posts and/or accounts that have been inactive for a while.