Technically the bolded part is wrong. Both merit and activity is needed to rank up. Previously activity was the sole determinant of the rank of the member. Now both of them are needed, only activity raising wont get you a new rank, you need to reach the corresponding merit too.
Consider this like a demarcation between those who actually post quality content and make thoughtful discussions on a thread rather than people who simply agree to every post. The former deserves merit on at least a few of their posts while the later do not. Thus they will lead the ranks and would be properly marked as "elderly" members of the forum.